2013 so far: The Last of Us (Runner up: BioShock Infinite)
2012: Sleeping Dogs (Runner up: The Walking Dead)
2011: Deus Ex: Human Revolution (Runner up: The Witcher 2)
2010: Mass Effect 2 (Runner up: Red Dead Redemption)
2009: Batman: Arkham Asylum (Runner up: Dragon Age: Origins)
2008: Three-way tie between GTA IV, Metal Gear Solid 4 and Dead Space. I enjoyed all three a lot, but none enough to choose it GOTY.
2007: BioShock (Runner up: Mass Effect)
2006: The Legend of Zelda: Twilight Princess (Runner up: Bully)
2005: Resident Evil 4 (Runner up: God of War)
2004: Metal Gear Solid 3 (Runner up: Half-Life 2)