REAL oldies, DOS games, that I still play from time to time:
Alien Legacy - I still daydream about how awesome it would be with modern graphics.
Another World - If you don't know it, you are not a gamer.
Elite 2-3 - Biggest gameworld to date, planet landing, trading, fighting, etc. Good times.
X-Wing/TIE-Fighter - Back when Lucastarts made good games.
Cannon Fodder 1-2 - great, mindless fun.
Fury of the Furries - good platformer.
Prince of Persia 1-2 - also great platform games.
Lemmings - One of the best of the old puzzle games.
Betrayal at Krondor - Never finished it, but give it a go from time to time, since it's an awesome RPG.
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Many others that I can't remember right now. I grew up with old games and regularly play them for nostalgia.