Ide say the best of 2008 would have to be left 4 dead, and far cry 2.... never could quite get into fallout 3 (especially considering the performance issues for me that were never patched...)
In 2009, Empire Total War and Starcraft 2 would have be high on my list. I would also say diablo 3, but I am almost positive there is no way its coming out in 2009.