Hard to decide, maybe Phantasy Star Online, but that's more for the people than the game. I love all the Final Fantasy games I've played (7 to 12, excluding 11), Borderlands, Morrowind/Oblivion/Skyrim and the Fable series
I see the sweat from someone's thinking has caused this site to crash again. It is so absurd how the youth imagine that being number 1 is so important when they haven't learned how someone who is number 1 thinks. *Quietly*