This is probably the first time in my time as a game fan I don't think I have a clear, established game of the year. I guess if you include Super Mario Galaxy 1, I'd say that was it, but it didn't come out in 2010.
I enjoyed Monkey Island 2: Special Edition for iphone, Game Dev Story for iphone, Megaman 10, Super Street Fighter IV, Super Mario Galaxy 2, Sin and Punishment 2, Red Dead Redemption, Dead Rising 2, Mass Effect 2, Ys III psp, KH: BBS, and some other games. All of which are pretty good stuff.
It's probably a toss up between SMG2, MI2 and RDR.
I think I'll just go with SMG proper.