Probably all the final fantasy games. I've never actually played any of them to the final end, played mostly FF7 and 8, always been so bored and then deleted/overwrited my old saves.
There are so many games that would be nice to try and play, but I don't have the time to test all of em.
System shock series for me...First fallout although i played the 2nd one. Any Medal of honor titles. (have a few but havent got around to playing them..lol) Missed a few of the world games series..(Was out YEARS ago, but was very fun)
IIgs? That was one of my first systems way back when. Defender of the crown was real fun on it (Wish cinemaware was still around, i miss their games)
the Battlefield 1942 games
the Medal of Honor games
Thief 2-3, I own both, but never got through them. Just too busy with school.
I'd never really heard of System Shock before, but it looks alright.
There are a ton of games I haven't played, but never felt the urge to go hunt them down, like all Final Fantasy games.
Oh, and for all you guys who are missing out on Diablo 2... get your butts to the store NOW and pick up the Battlechest. I can't believe everybody doesn't own the v1.0 cds. A good friend loaned me his discs (because my install disc was missing, and it was v1.3) tsk, tsk!