I'd have to say that my favorite PC game music was 1994's Betrayal at Krondor, for 4 reasons:
1) It was the very first CD game with CD quality music that I ever played
2) It sticks in my mind, because it gave me well over 120 hours of gameplay
(& I never did finish it!)
3) Even though it is 20 years old, I still have the copy I bought at CompUSA
on the shelf right here. I still think about trying to get it to play on Windows
7 once in a while.....
4) After playing this game, I completely got hooked on the Riftwar books by Raymond
Feist that this game is based on. This was the first time that a game introduced
me to a well written book universe.