1. Baldur's Gate I&II - best RPG ever created, with unmatched story and gameplay. I'm playing this at least twice a year.
2. KoTOR - magnificent piece of game and one of the best plot twists.
3. Diablo - lost most of my early teenage years over this, and do not regret a single second of it. Still the only multi game that I ever got into.
4. Starcraft - best story in RTS I have ever seen. Too bad, that Blizzard decided to take huge steaming dump on it since Wings of Liberty
5. Gothic I&II - marvelous. Love them and know every bit of it
6. Fallout 1&2 - in the realm of postapo, best shit ever. I wish a game lake this made from Metro 2033
7. Jade Empire - many do not know about it's existence, but I recommend it to everyone
8. Fable - really pleasant game, that I love to play from time to time
9. Disciples II - best turn based strategy. HoMM3 isn't even near it.
10. Zeus: Master of Olympus - nothing more relaxing (I have quite stressful job ;p) for me than to build some cities and go to sleep.
I'm not entirely sure, that these are the best games I have ever played. Maybe I do not remember them at the moment. Nevertheless they are all awesome, and I plan to play them till the end of my life ;]
Honorable mentions: F:NV, Settlers II, Atlantis, Etherlords, Broken Sword II, Mass Effect, Prototype, Morrowind, Sacred.
Yeah, and Torment is boring IMO. Never got into it.