4. Fallout 3 - Although I'm not too far into this game, it has already left a great impression on me. I look forward to finishing it.
3. Left 4 Dead - Co-op gaming at it's finest. This game does almost everything perfectly. It does need more content though...
2. Dead Space - Easily the most overlooked game of the year. This game should've made an impact on gamers on par with Bioshock and Half-Life. It really is that good.
1. WotLK expansion - Pretty easy pick for me. Blizzard really outdid themselves with this expansion and I'll likely be playing it for the next 2 years

Honerable mentions go to Rock Band 2, Guitar Hero: World Tour, and Gears of War 2. None of those made my list because, while great, none of them changed drastically from last year. I also feel a need to mention the expansion Command and Conquer: Kane's Wrath since it was a really, really good addition to the original game. Oh yeah, Lost Odyssey deserves some love too.
I'll be getting 2-3 games for Christmas, but I don't see my list really changing. (although I've heard great things about Fable 2)