New Rule:
As of 2.4, Daedric (and Aedric) weapons must have unlimited charges. Also, I've raised the base value of most of these artifacts to be much higher, and added the VendorNoSale keyword to the scary ones.
I have added USLEP dependancy in order to overwrite their added tempering recipe for the Ebony Blade.
I have imported USLEP fixes, which has improved some artifacts, such as Volendrung's added crit damage and Ebony Blade's missing quest stage which has been restored. Mostly, it fixes the abysmal bugs: inappropriate sound effects, etc.  I think its a real mod now. Thanks USLEP people!

Controversy:
As of 2.4, this mod increases the strength of the Nightingale Powers. While not strictly an edit of an artifact, these edits were made alongside edits to the Nightingale Armor Set, which I have raised to be on par with other Daedric Artifacts "in concept", and "in concept" the Nightingale powers and armor set go together as Nocturnal's Token and alternative to possessing the Skeleton Key. This is actually meaningless rambling, and I'm impressed that you're still reading it. Just know that your lack of approval for this decision, which I can feel from across time and space, has been rationalized away by me.



This mod edits unique artifacts and/or their enchantments and/or associated spells (and some tempering recipes) to make them frighteningly powerful, or in some cases to make them not completely useless, while ensuring at least one significant drawback to each, usually just by leaving some values vanilla.
I want my rare, legendary items to be game-changing tide-turners in my war against the hordes generated by ASIS, Higher Level Enemies Hardcore, Deadly Dragons and more, all powered by Combat Evolved. I've been careful not to touch anything that isn't the artifact or its enchantment or associated spells, (or tempering recipes or one hidden perk)  because I really want it to be compatible with the 184 other .esp files i use.

Ebony Mail, Masque of Clavicus Vile, Necromancer Amulet, Ring of Namira, Savior's Hide, Shield of Ysgramor, Spellbreaker, The White Phial, Auriel's Bow, Staff of Magnus, Volendrung, Ahzidal, Dukaan, Zahkriisos, Ebony Blade, Gauldur Amulet, Rueful Axe, Bloodskal Blade, Aetherial Shield, Auriel's Shield, Nightingale Armor Set, Mace of Molag Bal, Sanguine Rose, Dawnbreaker, Wabbajack and Wuuthrad are finished. Skull of Corruption is triple strength, but I haven't added the sweet evil clone spell to it. I've removed the Dragon Priest Masks, except for the dragonborn DLC ones, and placed them under optional files, because you may now choose between Normal Version and Improved Closefaced Helmets by navida1 Compatible Version!!

*Spoiler alert*
I just finished installing STEP Extended and a bunch of amazing mods to make my game hardcore and brutal. Imagine my disappointment when I got the Skull of Corruption. I murdered a man and stole people's dreams to get this power, and its weaker than my apprentice level destruction spells.
I've tried other artifact overhaul mods, but the balance was never quite right for me. There are some really cool ones out there, but I need to make my own.
Ironically, I haven't gotten around to the Skull of Corruption yet. (*edit* Took a glance at it and it might be more complex than i thought.)
I would prefer to replace the dream-stealing effect with the evil clone power from previous games. If anyone has any idea how to do that, I would love to incorporate that into my mod. Until I learn how to do that, I'll just jack up the power on the Skull and move on.


Presenting:
Better Artifacts! (working title)

I'm going to go through all the Daedric artifacts, Dragon Priest Masks and some other unique artifacts and at least triple their potency. That means the Skull of Corruption should do 150 damage in a wide area when juiced up with dream juice. That is, until someone teaches me how to replace that effect with the original Summon Evil Clone power that we all love.



Masque of Clavicus Vile:

The masque is already pretty good, but I raised the persuasion boost from 10 to 30, increased the weight (very heavy now) and now it can be tempered with Daedric smithing. Its stats are the same as a Daedric Helmet, but much heavier.


Ebony Mail

Boethiah really outdid himself/herself with this powerhouse. Armor stats changed to match Daedric Armor, but much heavier (suffer, mortal!). Can be tempered with Daedric smithing. That Poison Cloak ability does 15 damage/sec instead of 5.


Necromancer Amulet

I love this one. Mannimarco's tool for advanced necromancy has fallen into your hands. Like Callixto said, most people won't recognize the value of it, and 500 is the highest appraisal it'll get, assuming you have a hardcore barter system. I changed the Amulet by editing its description, and completely changed the enchantment on the amulet.
Old Enchantment: Conjuration spells 25% cheaper to cast, Magicka fortified by 50, Health and Stamina Regen reduced by 75%.
Weakness, thy name is Necromancer Amulet.
New Enchantment: My mod restores the Necromancer Amulet to its former lore-based glory.

Conjuration spells are 10% cheaper to cast. Magicka is fortified by 50. Stamina Regen is reduced by 80%. Total Health is reduced by 40 (ouch). Health regeneration is greatly increased.

Not bad, right? A nasty penalty, an underwhelming buff, and an interesting change to PC health. This amulet punishes you for wearing it.


These effects intensify when the PC's Conjuration Skill reaches 75!
Hot dog! This is a fun amulet! At Conjuration 75, the effects of the Necromancer Amulet are:
Conjuration spells are 60% cheaper to cast. Magicka is fortified by 200. Stamina Regen is reduced by 99%. Total Health is reduced by 120 (try not to die!). Health regeneration is cranked way up.

I'm not sure if the Health regen is balanced properly. Future versions may have a different value once I've tooled around with it for a while. I want it to be very fast health regeneration.

These magic effects are hidden in the UI because they made the enchantment's description ultra long and displayed in a tiny, tiny font. I wrote a simple description to replace the one I hid.

WARNING! This amulet can kill you. A Health reduction of 120 could instantly kill some characters. If your character's total health is 120 or lower and you are wearing this amulet, you will drop dead the moment you reach Conjuration skill level 75. I originally included a requirement that the PC's health must be at least 150 for the amulet to activate, but I removed it. Tell me what you think; maybe I'll put it back. I also wanted to include an armor rating boost or an armor spell or something, but I couldn't figure that out.

Extra bonus feature: The Blessing of Arkay will nullify the Necromancer Amulet's power. Arkay won't allow that kind of soul-bending magic. That's why Mannimarco and Arkay don't get along. Too weak to survive wearing the amulet, but love the fashion statement that it makes? Arkay will protect you while you show off at the club! Don't forget to take it off before the blessing fades!


Ring of Namira

One of the lesser Daedric artifacts, the Ring of Namira is fine as is. I raised the duration of Namira's Blessing from 5 to 30 mins.
I added a requirement to the enchantment and to the spell effects: it only works when the PC is not effected by Arkay's Blessing.
Arkay ain't havin' none of this. Don't try to pull one over on the God of Life. He knows about that guy you ate. He still loves you, though, because I don't want to edit the blessing effects in this mod.

When I do make a mod to change blessing effects, Arkay will kill you for owning the Ring of Namira, and all the divines will set you on fire (eternal, unextinguishable fire) if you are a vampire. That's how I had my oblivion game set up.


Savior's Hide

Hircine granted a mysterious pelt to someone who escaped his Hunting Grounds, probably as an afterthought. He didn't expect anyone to survive, and had to improvise a crappy daedric artifact on the spot to reward some poor bloke. Aforementioned bloke then fashioned the pelt into some decent leather-class light armor and had the local wizard enchant it with protection magic.

The Savior's Hide is a good candidate for ability tripling.
Resist Magic 45%
150 points of Resist Poison.
I removed the Ebony smithing keyword for tempering. Its daedric smithing now, baby!
The penalty for wearing The Savior's Hide is that you are wearing an ancient pelt. It smells musty, and it's equivalent to leather armor.


Shield of Ysgramor

Vanilla version is equal to an Orc shield and a little lighter. I'm satisfied. I'll keep the shield vanilla and triple the enchantment on it.
Resist Magic 60%
Fortify Health 60 points


Spellbreaker

My favorite daedric item, it's already the best shield in the world. I put the daedric smithing perk keyword on it and tripled the ward enchantment's potency.


The White Phial

Whichever potion type you choose to fill it with will be endlessly replenished. Thank Julianos that a Master Alchemist is offering to fill it up for me.

"I want to strengthen my magical skills"
Five minutes of Fortify Magicka 80 and fortify magicka regen 5%

"I want to deal more damage in battle"
Five minutes of Fortify One & Two handed weapons 50

"I want to be better hidden in the shadows"
Five minutes of Fortify Sneak and Pickpocket 50

"I want to be tougher in battle"
Five minutes of Fortify Stamina 80 and fortify stamina regen 15%

"I want to resist the forces of magic"
Five minutes of Resist Magic 60

"I'd like it to have the power of healing"
Five minutes of fortify health regen 50% and 100 points of healing


Auriel's Bow

This bow was made by an Aedra's father, who was also himself, or something. Basically, its the token of Anui-El, the karmic antithesis of Sithis.
See: Sithis Antithesis Theory, the Theorhetorically Antithetical Theory of Sithis.

The bow is in the Nordic class, with exceptionally high crit damage. I changed it to Daedric stats, leaving the high crit damage untouched. Added daedric smithing keyword as well. Its faster now, so you can unleash the wrath of heaven on some poor fools.

It also now has unlimited charges. And I multiplied the base value by ten.


Staff of Magnus

A really cool idea, it absorbs magicka at 20/sec until the target is down to 1 point, then begins to absorb health at 20/sec. Interesting and somewhat useful, its mid-range attack has more reach than most other concentration spells.
I increased the Absorb Health effect to 100/sec. If you've drained them of all magicka at 20/sec during the heat of battle, you've earned it.
I raised the base value and refigured the charge:effect ratio. It now holds 170 charges, but has an enormous gas tank.
Also updated the description to reflect the new spell.


Volendrung

It weighs a lot more now. Its stupid how heavy it is: 43. That's 13 higher than the ebony warhammer, to which this weapon is comparable.
I added the daedric smithing keyword for tempering.
Raised the stagger rate by 0.1.
Volendrung now has unlimited charges.
To the enchantment of Absorb Stamina 50, I added Absorb Health 20 and Paralyze 5 seconds. Welcome back, Volendrung.
FrankFamily suggested I do a "stone" shader effect on paralyze, and I like it a lot. I removed some of the script effects from the Absorb Health and Stamina on Volendrung, as well as the paralyze "green flash" to make it look cooler and less distracting. I didn't want to lose the "red and green flecks floating from the target to the player" effect, but it was necessary. You are still absorbing health and stamina, I assure you.


Ahzidal, Dukaan and Zahkriisos

Dragonborn adds three new dragon priest masks. I tripled the elemental resistence on their enchantments, added Fortify Shout Time 20% and removed their armor rating, armor designation and armor keywords, replacing them with 'clothing head' and 'clothing circlet' keywords.
Now the Mage Armor perk will function while wearing these mage-oriented masks.



I also changed the tempering recipe 'Workbench keyword' to 'NONE'. I am almost sure this will seemlessly remove the option to temper the masks from the game, but I haven't tested that yet. Tempering the masks probably wouldn't work because they have no armor rating or category, so I want to remove the option to temper from the menu. Crap, now i have to add Constructible Objects to the list of things I edited.

I also discovered this mod:
Ahzidal Dukaan Zahkriisos Retexture by Knight780

I think its the only mod that retextures only the dragonborn dlc dragonpriest masks, which was exactly what I needed to compliment either Unique Dragon Priest Masks - HD textures by skyrimaguas or Apophysis Dragon Priest Masks by pondcypress, both of which are neat retexures of the first 9 masks.


Dragon Priest Masks

There are two options in Optional Files. One of them is compatible with Improved Closefaced Helmets by navida1!

For Konahrik, I'm gonna check out this mod
Konahriks Privilege by Edhelsereg

and for Wooden Mask I'll try the main file from this mod and skip the update
Bromjunaar and the Wooden Mask by glemtvapen


Ebony Blade

I raised the weight to uncomfortable levels and slowed the speed way down (its a little faster than a warhammer). Changed reach and stagger to match regular greatswords. It has low damage, no crit damage and can't be tempered; I left those qualities untouched. The Absorb Health enchantment, which grows as you complete the daedric quest, now starts at 2 points and grows to 50 points. Vanilla started and 10 and grew to 30.


Skull of Corruption

It really should have an evil clone spell, but it doesn't. If I ever make another update to this mod, it will be to add an evil clone spell.

I just tripled the magnitude and area of effect for this artifact. Its likely to hit a lot of people now, and it drains 1 dream for every target struck. You'll drain it of dreams much faster now. It has unlimited enchantment charges, though.


Gauldur Amulet

This could've been just another weak artifact in Skyrim, but they just had to make such a big deal about how powerful it is. I had to make this amulet stronger because it was so weak it was immersion-breaking.
It was split into 3 pieces and sealed away, guarded by its draugerfied usurpers. People died to hide it, people died to find it, and apparently a lot of people died because it was used long ago. seems to me that it should boost magicka a whole lot in order to justify such a fuss.

I didn't mess with the fragments, but the united amulet is much stronger.

Fortify Health 60
Fortify Magicka 120
Fortify Stamina 30
Fortify Carry Weight 15

The base value is 10 times higher, and I changed the weight from 0 to 0.5.


Dwarven Bow of Fate

I like fun, unique enchantments. I just want them to be strong.
This bow is slightly stronger than Dwarven, which is pretty bad. Its enchantment does 3 separate 50% chances to absorb 25 Health, Magicka or Stamina (that's one chance for each stat, if I'm being confusing. A one-in-eight chance of getting all three in one shot!)

I increased the power to:
50% chance to Absorb 50 Health
50% chance to Absorb 100 Magicka
50% chance to Absorb 200 Stamina

I added a zero to its base value, as well, in case selling it is what your character needs. It still has 22 charges and the same capacity to hold them.



Rueful Axe

I want this weapon to be a viable alternative to Vile's Masque, instead of something you hold for a while before getting the good thing. If you choose the axe, its a whole unique quest ending with dialogue and everything. Let's make that axe worthwhile!

First of all, the stats are odd. Its extremely light, and the slowest melee weapon in the game. This doesn't jive with me. Since its slightly weaker than an Ebony Battleaxe, I'll make it slightly heavier than one, too.

Secondly, it doesn't do anything special against werewolves, which I thought was odd. I added the same script that silver swords have. It gives the player a hidden perk while equipped that deals 20 extra damage to undead and werewolves, and I believe vampires have been added to that list by unoffical patch. I also changed the tempering recipe to be tempered with silver now. Its silver now, ok? Deal with it. Benefits from Daedric Smithing perk.

The enchantment, a lackluster damage stamina 20, has been upgraded to a thrilling Absorb Stamina 20, and the axe now has unlimited charges, like some kind of freak. Its still the slowest weapon in the game, possibly the universe.

Multiplied the base value by ten.


Bloodskal Blade

Bethesda must've held a focus group to ask five-year-olds what skyrim was missing. They said, "A sword that shoots energy beams!"

Its a pretty cool looking effect, and I'd like to use it as a part of an advanced magical arsenal. I just needed to make it stronger...

This sword has a few different things going on.

The "Red Glow" effect, which does... something... now has added to it a medium strength Frost Damage enchantment because lore, apparently. 50 charges.

The energy waves that are emmitted during a power attack have two forms: horizontal and vertical waves. Horizontal is 90, vertical is 120 damage. Unleash the brave reckless gods within!

This sword is of silver make. It follows that someone like me is going to add the SilverSwordScript to it so that it can do extra damage to those weak to silver. And so i did. I also multiplied the base value by ten.



Aetherial Shield

I've never picked this shield, but it seems interesting. The bash does high level calm and fear in addition to etherializing the target. Other than that, its just a dumb dwemer shield.

I made it as light as a bonemold shield and as tough as an orcish shield. It benefits from Dwarven smithing perk. Multiplied the base value by 5.


Auriel's Shield

Just like the bow, I've raised the stats up to Daedric levels and added the daedric smithing keyword.
I don't want to have to choose between fun enchantments and the superior gear I can make at a forge for myself. I multiplied the base value by 10.


Nightingale Armor Set

Hey, did you know that if you get the Nightingale armor too early in the game you only get a low-level version of its enchantments? That's dumb. I raised all the lower level versions of the enchantments to be just as strong as the high-level version, plus boosted its Fortify Stamina and Fortify Illusion effects to be much stronger.
That's Fortify Stamina 60 and Fortify Illusion 30. Everything else is vanilla for level 32, no matter what level you are!
Also, the cuirass wasn't on par with the rest of the set, so I improved it to match the quality of the other pieces of the set. I also added the Daedric Smithing perk to the keywords for the whole set.

Bonus feature: I've tripled the strength of each of the three special nightingale powers that Nocturnal can bestow.


Mace of Molag Bal

Apparently you can't have an artifact overhaul mod without tweaking this mace. Its already really awesome, but it looks like the damage magicka and damage stamina effects need to be changed to Absorb Magicka and Stamina, and the Soul Trap can be turned down to 1 second duration.

Obviously, I'm going to make it way too heavy, to punish you, and I'll slow the speed down a bit and increase the damage a tad to balance this. Also, the Mace of Molag Bal now has unlimited charges. Why not?

I added the Daedric Smithing perk keyword, and also added the VendorNoSale keyword, because no one wants the token of the deity of horrible, unmentionable crap. The fact that its more valuable now it meaningless.


Sanguine Rose

A fairly handy staff, this daedric artifact summons a leveled dremora.

I tripled the duration of the spell, and changed it to refer to a new leveled list I made that includes archer and mage class dremoras, as well as the standard melee guys. It also has unlimited charges.


Dawnbreaker

Unlimited charges. Increased base value and added Daedric Smithing keyword.


Wabbajack

Unlimited charges. Added VendorNoSale keyword.


Wuuthrad

Raised "bonus damage to elves" effect from 20% to 40%. Raised base value. Imported USLEP fixes make this weapon very useful.


Changelog:
v1.0 Finished Ebony Mail, Masque of Clavicus Vile and Necromancer Amulet.
v1.1 Cranked up the health regeneration on Necromancer Amulet to be stronger than Ring of Namira
v1.2 Ring of Namira added
Savior's Hide added
Shield of Ysgramor added
Spellbreaker added
The White Phial added
Auriel's Bow added
Staff of Magnus added
Volendrung added

v1.3 Ahzidal added
Dukaan added
Zahkriisos added

v1.4 Hevnoraak added
Krosis added
Morokei added
Nahkriin added
Otar added
Rahgot added
Vokun added
Volsung added
Ebony Blade added

v2.0 Hevnoraak, Krosis, Morokei, Nahkriin, Otar, Rahgot, Vokun and Volsung removed because I like improved closefaced helmets more.
Skull of Corruption added
The Gauldur Amulet added

v2.1 Adjusted the monetary value of the Necromancer Amulet to match the unidentified amulet from the Blood on the Ice quest. They both have base value of 1000.
Added requirement to the Ring of Namira ability. It now deactiviates when the PC is effected by Arkay's Blessing, just like my Necromancer Amulet does.

v2.2 Fixed The Gauldur Amulet's description and added 15 points fortify carry weight. Multiplied the base value by 10 and changed the weight to 0.5. Also, used TESVEdit to sort masters. Sorry about that.

v2.3 Small typo fixed.
Added Fortify Shout Time 20% to Ahzidal, Dukaan and Zahkriisos.
Previously removed Dragon Priest Masks are uploaded as an optional file. There's a Improved Closefaced Helmets by navida1 compatible version available!!

v2.4 Dwarven Bow of Fate added
Rueful Axe added
Bloodskal Blade added
Aetherial Shield added
Auriel's Shield added
Gave Daedric (and Aedric) weapons unlimited charges and raised base monetary values.
Nightingale Armor Set added
Nocturnal Powers added
Mace of Molag Bal added
Sanguine Rose added
Dawnbreaker added
Wabbajack added
Wuuthrad added
Increased Volendrung's stagger rate and changed the shader effects on the enchantment to do a 'stoneflesh' on paralyze. Thanks for the idea FrankFamily! I had to disable the "red and green bits floating from the target to the player" effect (Volendrung only, no great loss). I deactivated the paralyze "green flash" as well. Volendrung does have a green paralyze weapon shader, just like in oblivion.
Ebony Blade Absorb Health effect increased to 64 points. Added USLEP dependancy to overwrite the Ebony Blade's tempering recipe added by USLEP. No tempering allowed!
USLEP fixes imported, making some changes like adding crit damage to Volundrug and adding a whole extra stage of growth to Ebony Blade. Any trait of an artifact mentioned in my readme is unchanged by this. I did allow USLEP to add a tempering recipe for Shield of Ysgramor, and updated the readme.