1. Dragon Age: Origins
Went in with little expectations, and came out of my first playthrough reminded why I bought it in the first place: Bioware is really good with their storytelling. It became more of a #1 as I went through my second playthrough, experimenting with different decisions and realizing how much can differ in any one playthrough. If I had more time, I would even tackle a third playthrough, but ME2 is less than a month out.
While I enjoyed Fallout 3 last year, there was a bit of desire that I had for a more action oriented FPS/RPG game. This satisfied that itch and some.
Probably the best open world game I've played in terms of gameplay to date, and the while the story seemed to disappear during the middle portion of the game, it came back really well at the end, making me drop my controller due to the shocking truth of that final twist, and wanting more.
4. Killzone 2
While the single player campaign was kind of dull, the multiplayer was where most of my enjoyment with this game was. The consistently changing objectives was such a great way to blend all types of FPS multiplayer modes into one, and I would love to see this style built upon (and better received by people who just want TDM) in the future.
5. Assassin's Creed II
Just finished this one in time, and wow, this game is leagues above the first Assassin's Creed. With the gameplay and game structure much better refined from the first, and the story going in some crazy places towards the end, the idea of an AC3 doesn't seem as strange to me now as AC2 seemed after finishing AC1.
6. Batman: Arkham Asylum
Yes, I saw the Dark Knight last year. Not a huge Batman fan either. But this game is a much better Batman story than TDK will ever be, and an outstanding game as well. The only things that keep this game on the bottom half of my list(other than personal tastes) are the boss battle structures.
7. Shadow Complex
While I enjoy the "Metroidvania" style games, there was something about this one that pulled me in for the few days after its release. Playing through three and a half times to get that level 50 achievement was an experience that I would've payed more than just $15 for.
8. Modern Warfare 2
Fun fact: I was 1 year late to the COD4 party. So after playing catch up, I saw what all the COD4 buzz was about and could see why the hype was there for MW2. Say what you will about it, some games are popular for a reason.
10. Uncharted 2: Among Thieves
The "cinematic" parts of this game were incredible, but even with it's improvements to gameplay from the first, there is still some tweaking needed to be done, which is why this only sits at #10.