Well-thought-out and creative. There are a lot of cards that have synergy (like Milandra and any that gained stats upon digestion), making it more fun to combine their abilities. Some combinations utterly break the game, but they take a bit of work to discover. The power-ups are a brilliant idea, and (though some are a little expensive) well worth getting in order to give your team the boost they need.

One small thing: I didn't know you could combine cards of the same type (playing a duplicate of a pred on one already in play) in order to level them up until I did so by accident. I don't think that's mentioned explicitly in the game, but it was an interesting little tidbit, if slightly obscure.