That is a tough call on Top 10. I personally have an eclectic taste and would be able to name but a few offhand.
1. Dungeon Keeper A great concept to play the malevolent villian against the goody two shoes heroes for a change. I regret however many a lowly worker was slapped to death when I demanded my way.
2. Fallout Post Apocalyptic game that is still to this date an enjoyable turn-based game. I being a old school Tabletop RPG fan loved the incorporation of the GURPS system.
3. Dark Forces 2 While I did enjoy the storyline of the original, the first person view did give me quite the headache and I was thrilled at the 3rd person view option of its sequel. Also I thoroughly enjoyed when MSN had pc-game servers up for 4-8 person combat scenarios. Hell even capture the flag was fun with this game.