Empire: Total War was my greatest heartbreak ever.
I'm going to say Dragon Age: Origins, just because there's nothing better. It's still a good game but probably not GOTY material due to the repetitive gameplay, though the characters are likable and the plot is attractive enough to warrant putting up with the flaws to see it to the end. Arkham Asylum runs terribly on my PC; seems like a solid game, but no comment on that. L4D2 isn't enough to warrant a separate game. Haven't gotten enough of a feel of HoI3 to say anything definitive about that. Assassin's Creed 2 is so very boring, but its acronym makes me want to dig out Armored Core 2 and play that; so there's a positive, I guess. Modern Warfare 2 is bad. Haven't played the sequel to the Penny Arcade adventures yet, if the second episode came out in 2009 (can't remember, too lazy to check).