1. MASS EFFECT - 'nuff said.
2. Bioshock - Great game. Best "oh snap" moment I think I've ever had in a game.
3. Call of Duty 4 - I'm suprised at how much I liked it.
4. Supreme Commander (and Forged Alliance expansion) - Pure RTS awesomeness.
5. Ace Combat Six - Ace Combat Awesomeness on the 360.
6. Assassin's Creed - Not as spectacular as it should be, but still fun.
7. Elder Scrolls IV: Oblivion - I still haven't gotten around to beating the game yet.
8. Crackdown - Great co-op multiplayer. If only they'd make Crackdown 2 and add aerial vehicles and boats.
9. the .hack//G.U. games - .hack rules, period. I still need to finish Vol. 3... been sidetracked with the 360 games.
10. Hitman: Blood Money - My first Hitman game, and I enjoyed it. After playing the Kane & Lynch demo, I'm worried about the next Hitman game.
Honorable mention: Sins of a Solar Empire - Still in beta, but it's just plain awesome. When the Star Wars mod is released, it will rule them all.