I have a ton of games I'd consider in my top 10 but there would be 50+ of them over the last 25 years+ of gaming ... here are a few I can remember off hand.
In no describable order.
Powerdroid 90 (would make an excellent XBLA / flash game now imo)
Sensible Soccer (most amazing control ever, for a 4 way joystick and one button)
Deus Ex (best RPG to date, second would probably be System shock)
Captive (if you have never played it or heard about it then you missed a golden game)
Hired Guns (awesome four play co-op game 2x amiga 500 linked together with 2 players each .... awesome awesome fun beyond words)
Quake 2- MP mostly (golden age of FPS for me ...CTF, KOTH, 3WCTF, QCCL, Team fortress, Action quake... need I go on?)
Lotus Esprit (sometimes called Esprit Turbo challenge in odd places

).
Dark Age of camelot (first and only MMO to achieve decent PVP)
Call of duty 2 (awesome community and clan base)
Call of duty 4 : Modern Warfare (yes I went there, oh yes and I still do, awesome single player story and trend setting be it good or bad multiplayer that is copied over and over even by non-activision flunkies).