To play game so excessively that you're no longer playing a game, but being played by a game. The condition is often accompanied by symptoms such as talking about games excessively, especially of their trophies(PS3)/ achievements(XBOX360), and general disregard and neglect to surrounding environment called life.
Mark: Hey guess what guys, I got all the achievements for COD World at War, and I got my 3Billionth kill!!
Steve: Mate, you are so gamed.