planescape: torment - i am convinced that, to this day, PS:T has the best story in any RPG. oh, the sparklies were shiny enough but the story is what sets it apart, in my opinion. and since i'm a bookworm, the complaint that there was too much reading meant nothing to me. they got an amazing cast to do voicework on the game (sheena easton, hello!). and, really, "what can change the nature of a man?"
sid meier's alpha centuri - let's be honest: it was brian reynolds' work. to me, it was a better execution of civilization than any of the civilization games. the faction leaders had more personalities and more distinctive personalities than civ (miriam and yang are always marked for immediate death in my game). unit designs definitely gives you a greater attachment to the game/units. and santiago was just hawt.
jagged alliance 2 - alas, poor sir-tech (RIP)! i knew them, a company of infinite jest, of most excellent fancy. they had to have been one of the best small development house. ever. the game had tons of humour (a hallmark of sir-tech) to go along with just plain entertaining gameplay.
master of orion 2 - still holds up amazingly well. still amazingly fun. frequently imitated, as of yet not duplicated.
torchlight - a wonderful diablo 2 clone that just plain works well. tons of replayability and just entertaining.
football manager (formerly championship manager) - the whole series, really. even if you dislike football/soccer, the game is still absolutely amazing. you are the manager, naturally, of a football club and you have to decide who plays and how. you have to manage your money and the personality of the players all while dealing with the rest of the game world. another game where 7AM arrives way too soon.
world of warcraft - even though i intentionally limit my exposure/access to the game, it's still amazing, a terrific execution of the concept.