Super Mario Glaxy
Although I generally prefer more violent games like CoD4 and left 4 dead, this game is my personal best game of all time, because it managed to truly innovate the platform genre, by evolving the very concept of level design in ways no one thought possible, and you could honestly never predict what was coming next.
Now, you might say that mario 64 did the same thing, but aside from being in 3-D, there was no real innovation. You could predict the levels so easily, it wasn't even funny. Lava level? Check. Underwater level? Check. Ice level? Yawn....
Galaxy had some of these same level ideas, but managed to reinvent them. How often have you seen a fire level and an ice level combined into one? In the aforementioned underwater level, just when you are starting to get bored, you are launched onto a giant twisting stone pathway in the sky, defying gravity every step of the way. And one later level has platforms disappearing from reality and back, forcing you to rethink your hardwired gamre senses in order to get through.
When I first got Galaxy, I was in constant anticipation, wondering what would come next, and if I could relive each of the amazingly creative levels anew each day, I would be very happy. Right now the best I can do is buy Galaxy 2 for another "hit" of innovation.