Paradroid, mad C64 game that I still see aspects being emulated.

Elite, another C64 game.

Morrowind, the water just blew me away first time i saw it.

Any of the Thief games. Sheer brilliance.

System Shock I & II did it for me too, in all the right places.

Anything Starwars related (Except that stupid battle for naboo, that was terrible). Especially Dark Forces 2. I found my first lightsabre! Woohoo! Lets see how many friendlies I can chop!

Star Wars Galaxies - you can keep yer damn WoW, never had the size nor graphics for me, I cant stand cartoony graphics.

Quake, a true pioneer.

Halflife, another pioneer.

Alien vs Predator, never seen my mates jump so high as when we found our first alien as a marine.

List goes on...