System Shock 2 is awesome. It is probably starting to look a bit dated now, but I know there is a group of people doing or have done a mod to improve the graphics. Mostly to create higher polygon models and better textures if I recall correctly. I think I will go see if I can find it. It would be worth playing again if they finished the graphics upgrade.
EDIT: The links were easy enough to find. The first is for the models and the 2nd for the textures
http://perso.wanadoo.fr/etienne.aube...ck_rebirth.htm
http://texturemod.wz.cz/