1. Portal (clever design and pitch black humour ftw)
2. The Witcher (a superb RPG)
3. Episode 2 (Alyx rocks)
4. Bioshock (good shooter with a nice story)
5. Audiosurf
6. Medieval II
7. Mass Effect
8. Episode 1
9. Team Fortress II
10. PlanetSide (although released in 2003, I had a lot of fun with that unique MMOFPS from 06 to 08 )
Disappointment of the year: Spore. What a cruel lack of depth.