Honestly, 2007 and 2011 were two of the best, if not the best, years in gaming.
My picks:
2006: Okami
2007: Super Mario Galaxy
2008: Grand Theft Auto IV
2009: Uncharted 2: Among Thieves
2010: Super Mario Galaxy 2
2011: Batman: Arkham City
2012: Xenoblade Chronicles
2013: The Last of Us
2014...