Ascension is a very good video game adaptation of one of the best tabletop competitive deck-building games, Ascension: Chronicles of the Godslayer. One player (with AI players) to four players can play locally (hot seat) or online (you must register for a free Asmodee online account), which allows cross-platform play (between Steam and various smartphone implementations).

The game
You start with the now-standard deck-builder set-up - 10 cards - and you draw back up to five cards at the end of each turn. Cards in the base game can be heroes (played once and discarded), constructs (semi-permanent), and monsters (defeat for points). Heroes and constructs generate two of the resources in the game: Runes (money for purchasing cards) and/or Power (fighting strength). Defeated monsters award you Honor (victory) points. You play cards on your turn, which generate Runes and/or Power, and you spend those to acquire or defeat cards that have been dealt from the shuffled "Portal Deck." In addition to the minimum-six cards in the Portal Deck, there are always at least three other cards available on the side: two inexpensive heroes to buy, and one monster to fight. Heroes and constructs are worth some amount of Honor, while defeating monsters draws Honor points from the Honor pool. The Honor pool works as a timer for the game: at the start of the game, Honor is placed in the pool, and the final round completes when the last Honor points are drawn from the pool. Then the value of the heroes and constructs is added to the Honor points, and the player with the highest total wins.

Expansions
The base game is great, with a lot of cards and four factions with different emphases (green for earning Honor, blue for drawing cards, brown for constructs, and purple for Power/destroying cards). But there are a lot of expansions produced for the game, including some (the Portal Promo Pack) that don't exist for the tabletop version. Each expansion you get enables the option to add cards to the Portal Deck; the card sets can be toggled on and off at game set-up. Several expansions add new rule variations to the game, like Energy Shards (in Rise of Vigil), faction champions (in Rise of Champions), or Insight (in Dreamscape). Expansions add so much variety to the game that I highly recommend you buy Ascension as a combination package if you can.

Single-player
There is no campaign in Ascension, and no gradation of difficulty. Each game of Ascension you play is discrete from any other. You can play with one to three AI players, and you can select a broad strategy for each AI player separately: try to win by fighting monsters (red), or try to win by getting valuable cards (green). AI is good, though the fighting deck AI is a little stronger/more difficult to beat. When playing locally (single-player or hot seat multiplayer), you can add points to the initial Honor pool to make the game last longer, for additional practice or to allow for bigger and bigger combos.

Multi-player
Hot seat play is supported, and you can mix and match human and AI opponents for some added variability. Online play happens through the Asmodee digital web site, which means you can play with anybody using any version of the video game, though all players must have the same expansions if you opt to include expansions. NOTE: separate licensing for each platform means that expansions you buy on Steam will NOT show up on your phone and vice versa.

The online community is robust and active. There are dozens of people online at any time, starting games every minute. Online games cannot modify the starting Honor pool, and online games have a time limit that you choose at the outset, from 10 minutes (a hyper-fast game) all the way to the leisurely 28 days. Each player has a clock that counts down their time, that starts when it is their turn and pauses only when it is another player's turn. If you run out of time, you forfeit the game. Your online profile tracks how many games you've won and lost; games that others forfeit count as wins for you, games you forfeit count as losses. I recommend that new players select a half hour MINIMUM (an hour preferred), even when playing live at the computer: you'll need time just to read the cards, and it stinks to forfeit a game involuntarily.

Achievements
There are a LOT of Steam achievements for Ascension. Some of them are straightforward - win X number of games, for instance - but many of them really feel like monumental achievements because they are so difficult to achieve. Many are difficult because they require a certain combination of cards to become available in a game which is intrinsically random. I like this, because it makes the achievements rare, but it means that you cannot force these achievements through skill or perseverance alone.

Summary
I am very happy with the Steam adaptation of Ascension and recommend it highly to any gamer interested in competitive card games.