I'm surprised to not see any games of the decade, but then you remember sooo many great games to come out over the past two generations of consoles. I still haven't played some only because I've never owned a Playstation (1, 2, or 3). So instead, I'll post some of my favorite franchises of this past decade...   
 
In alphabetical order: 
Assassin's Creed  
Burnout 
Call of Duty 
Fable 
Grand Theft Auto 
Halo 
Mass Effect  
Rock Band 
Star Wars: Knights of the Old Republic