I think Gears of War 2 is the best system link multiplayer game ever so it gets my GoY 2008. The Amped Energy drink game tour just ran through my college and had 8 360's linked for Gears 2. That was sooo much fun, pure pwnage.
fallout 3 just ahead of gears 2. GTA well overated in my opinion. not as much fun as San Andreas and giving it a more serious storyline didn't make sense, Niko is racked with remorse about his criminal life and feels guilty about killing story characters but will happily mow down pedestrians and blow away innocent bystanders.