Half-Life 2. When this game came out, I played it and was absolutely blown away. The plot is fantastic and immediately hooked me. It was also the first game that I played where they heavily featured physics puzzles and it blew my teenage mind. "Rise and shine, Mr. Freeman. Rise and shine."

I spent SO many hours playing Diablo 2. Not EverQuest hours but pretty high up there. Being an alt-aholic, I never actually ended up getting a level 99 (I think my highest was a 96 Amazon) but I spent SO many hours playing. Doing MF runs, PVPing outside of Act 1 Camp, Cowlevels.