This was tough for me, as Dragon Age, Batman: AA, and AC2 are all fighting it out. Gun to my head, I'd go:
1. AC2
2. Batman
3. Dragon Age
4. UC2
5. Ratchet & Clank: Crack in Time
6. MW2
Call me crazy, but MW2 just didn't do it for me like CoD4 did. I know that some of those on the list are sequels, but something about those above MW2 felt more fresh to me.