For me, it was the game Rocket Jockey released by Sega Soft in '96. It was perfect. The game featured a surf rock soundtrack by Dick Dale. The entire premise of the game was to ride around on rockets and using long cables to yank your opponents off theirs. Referees were also fair play. I don’t think I’ve met anyone else who has played the game, so if you have, let me know!
ID games of course (Keen/Wolf3d/Doom), Sim City series. Raptor, Warcraft I&II, LucasArts games.
I was totally sucked into the world when I first played it as a kid. The balance and trade offs between tech and magic are awesome and the incredible dialogue and (OK from what I remember) story makes this one I come back to every once in a while.
I don’t think I ever actually have beaten the game though – but I do that with nearly every game.
Scorched Earth Worms UT2K Quake 3 Arena Tribes Descent Mechwarrior 2 Mercenaries You Don’t Know Jack Where in the World is Carmen San Diego
Theme Hospital I still go back to on occasion. I’ve seen Two Point but it’s not the same.
Star Control 2 Starflight Civilization Railroad Tycoon SimCity Pirates! King’s Quest Space Quest Telengard Lemmings
My childhood! :-)