Basic Description: Each player picks a hero. The hero comes with a 40 card deck that you use to play that hero. You play against a villain (which has their own deck) and it's set in an environment (which is also represented by a deck).
The heroes work together to defeat the villain, it's cooperative. If at least one hero is still standing and the villain goes down, the heroes win.
More complex description: While the concept sounds simple, the execution is much more complex. Some villains have alternate victory (or lose) conditions. Baron Blade, an often suggested first villain, wins if he successfully pulls the Moon into the Earth. The how is described on his character card, but basically it's a countdown timer. If you don't deal with him fast enough, he wins. If you do deal with him, you haven't won yet, now you have to deal with his other side of the character (every villain has a condition that flips their card) and now he just tries to pound you into the dirt.
Every villain is pretty different, using very simple concepts to really make huge differences between them.
The heroes are also pretty different. Broadly they come in two categories, support and damage, though some provide both. Heroes also mix and match very differently. Playing Ra alongside Absolute Zero is a lot different than playing Ra with Fanatic, which is different than Ra paired up with Legacy.
Not to mention the environment decks. Each has various cards that either help/hurt the heroes, but depending on the villain/hero set up, a card might be helpful, while other times it's painful. Also, certain environments make villains much tougher, while other environments will make them easier.
All in all, there are several reasons to buy/play this game:
1) You like comic book themed games
It's not licensed on anything, but the art is really good and very representative of comic book art. The villains vs hero concept of the silver age of comics is expertly represented both in the art and the game play. If you're familiar with comics you see a lot of similarity between various Marvel and DC characters in this game, but once you look past that, you'll also see nuance about the characters that could actually make for some cool comic books in their own right.
2) You like cooperative games
I like competitive ones, but cooperative games are fun too. Coop games have to tread a really fine line of difficulty, often times once you know how to beat a game it really isn't much of a challenge and you lose interest in it. This game solves that problem brilliantly. All the combinations provide huge differences in difficulty, plus it vastly increases replayability. The randomness of card decks help provide some uncertainty as well.
3) You just like good card/board games
It's really well put together. Cards have a really good layout, though a couple have complex sentence structure that I find off-putting with their font. The rules are very simple at their most basic. Your turn goes: Play a card, use a power, draw a card. It often gets modified very quickly (as card games tend to do) by card text. Overall the rules design is very streamlined and a basic understanding of card game logic will serve you well 95% of the time. The only downside is that the rulebook isn't the best, but that's a common complain about most games.
They just did another print run. If it sounds interesting, get it quick before it disappears. The company has said they don't plan to keep reprinting this game. It's $40 for the base game and if you aren't thrilled with it, you can probably resell/trade it at a reasonable rate.