My biggest time sink game wise in my life is without a doubt Everquest. I played from May 6, 1999 to June 1, 2010. For the first 5 years, my game time averaged 12 hours a day. That comes up to almost 22000 hours and thats just the first 5 years. I literally had no life.
My second game would be another MMO: Dungeons and Dragons online. I played that game for about 15 months.
After that would be a toss up on some console games. Diablo III, Final fantasy VI, Dragon quest VIII, SMB 3, Ni no Kuni.