There's not 1 game that I can honestly say is the 'best I've ever played'. The first PC game I bought myself was AoE II, I have good memories of those times so it's ranked quite high on my list.
Games I spent countless hours on is Diablo II, UT2004, Warcraft III. Good times!
My current favourite is probably Bioshock, but that's only because I'm busy with it at the moment...
