Only two spring to mind, ME3 and Dishonored, and with no disrespect intended, I don't think either are good enough for a GOTY. The tragedy is that there's nothing else this year at all even close to worthy either. Considering last year gave us Skyrim and DE: Human Revolution, both GsOTY in my opinion, this year is dreadfully lacking in quality games.
Other candidates would be...what? Diablo 3, Max Payne 3, Borderlands 2? Not played any of them but just no, across the board.
Bah, fine, Dishonored then; there's nothing else coming out this year that will be noteworthy. In it's favour it's a polished, beautifully crafted and clever game with a great aesthetic and immersion. It was an original title in a year of never-ending sequels. It falls short of it's true potential however for numerous reasons. Not a true master-piece, but came very close.
If I could really choose, I would give it to DE: HR, Skyrim or Saint's Row 3, all Q4 2011 releases, but all three orders of magnitude better than anything released this year. Also, a pre-emptive honorary GOTY for Project Eternity.
