Did you finish Subnautica and do you want 20-40 hours more of the same? Do you also not mind that the game doesn't quite reach the same level of excellency as the first game (but is still very good)? Then this game is for you. If you haven't played the first Subnautica yet ... well, what are you reading this for? Go and play it, it is fantastic. And I'm usually not even much into survival games.
This one isn't quite as strong, but falling short of one of the best games ever made is not something to be overly ashamed of, it is still very very good. The game has a smaller scope and clearly had a lot less development and polishing time than the first game. While the first game certainly wasn't bug free this one has a lot more - sounds not playing, instruments not working (restarting the game fixes that), resources placed in such a way that they can't be picked up, some visible places without texturemaps ... and the first time I deployed my shiny new Snowfox it dropped straight through the floor. (I ended up making sure to look upwards while deploying it to make sure it spawns above the ground collision ... either that helped or I just managed to find that one wonky spot on first deployment)
The mystery story was also weaker than in the first game - due to it being set on the same planet there is less of the unknown in general, but the story is also split. The part of the story regarding the reason why you came to the planet in the first place is mostly resolved after less than half of the game, the other half of the game is very interesting but also very straightforward and culminates in an unnecessarily big cliffhanger. The first game was a lot more sophisticated in telling and ending its story. And also a lot more robust when it came to accidentally doing things out of the intended order, I had at least one very weird interaction that was clearly not supposed to happen that way. (But any more detail would spoil things)
A lot more of the game is set on dry land and while I certainly liked a lot of it I also think these aspects could have been done better. As beautiful as these arctic areas are, navigation is a lot harder on dry land and clearly not something the leveldesigners where as comfortable with as they are below the surface, the areas flow and guide the player a lot less. Cold as a hazard takes a lot of waiting at first and is a complete non issue later on ... and let's not even talk about the logic of temperature in this game. I'd say the dry land sections were at the same time a touch too big and a touch to underdeveloped.
But despite all of these issues the game often absolutely nails the feeling of wonder and discovery that made the first game so damn good, the visuals, the sound design and the music play together wonderfully and had me just staring in awe multiple times and in the end, that is a large part of what makes these games so great.

Unfortunately this one lacks the magic of the first installment. I don't know what breaks the game for me - perhaps the fact that you are close in land? That you get to encounter another human in said land as early as you land? and then it is pretty much the same early grind for materials. But without the immersity.

Overall a big downgrade from the original, still a good game just because it's a subnautica game.

Map is 1/6th the size of the original, all but two biomes are bland and boring where in the original everything was beautiful.

The story was poorly made and boring, you constantly had characters you didn't like yapping in your ear (Alan carried the story) then they made you go back and forth to the most random areas for the cashes and body cashes. The only decent part of the story was the final cutscene and even then it was impressive because of the visuals, and curiosity. You felt no connection to the planet at all.
In the original it was never forced upon you but you wanted to progress it willingly out of curiosity. To follow the Degazi base and see what became of them, etc and it was pretty intuitive where to go just keep going deeper into grand new biomes such as your last dive with the lost river and lava zones. At the end you really felt like you had grown to like 4546B.

Game was filled with bugs, lillypad islands had outcrops and table coral inside the islands, invisible hitboxes, my snowfox fell through the mfing map...

Leviathans were not scary at all, the shadow leviathan which was the scariest probably resembled more of a electric eel or river prowler rather than a reaper or ghost leviathan. Also for some reason you get the perimiter defence module at the beginning which doesn't help in making them feel like chums especially since all leviathans grab you in this game.
In the original only the reaper grabs your vehicle but even then reapers were terrifying. Also in the original the leviathans had iconic and terrifying roars, in this literally every creature has a loud ass roar and the leviathans roars are less intimidating than the stalker or boneshark equivalents in this game?

The music was nowhere as good as the original but it was still decent.

Probably the only good thing that came from this game were the new building options that make your base really feel like a home. But also a LOT of invisible hitboxes kept messing up building which is unfortunate.

I hope for Subnautica 2 they keep the building improvements but revert back to the original in many aspects.

Subnautica below zero is not a bad game, I'm just harsh on it because of it's godly predecessor is. If you are a fan of the original I can only guarantee you'll enjoy the first 5 hours of it and base building. If you're new to Subnautica play the original.