I've been addicted to this game for the last week.
It is a mix of collectable card games like Yu Gi Oh or M:TG. However, unlike most CCGs, you do not have to BUY the booster packs either through in game currency or real money. You earn them through the gameplay which is a major bonus to me.
The story is better than you would expect from a game of this genre as well. If you choose to, you can find that every person you come across has several (sometimes more than a dozen) different things they will say to you. And what they say will change depending on whether or not you have defeated them yet.
The actual gameplay is quite balanced. As you get stronger, so does the opponents. And there are many different strategies you must use. Going all out offense will work sometimes, but some characters are built to counter with good defense and the ability to disable your best cards at just the right times. You must choose your deck wisely depending on your opponent. This depth is part of what makes this game so fun.
The art style may turn some people off but I think it's very endearing and original. I don't know any of the indie games that this takes it's characters from but it's cartoonish and quirky and simple and it fits the overall mood of the game.
The best part of the whole game however must be the music. Everything from the menu screen, to the various places you visit, to the battles have music that is perfect for the situation. It's soothing and it's energizing at the same time. This, along with the humor of the game, and the visual styling make this a game you will never want to put down.
Although I have not beaten it yet, I know from reading around that the game has more things to accomplish even after you defeat the 'final boss'. So replay value is strong here too.