Yeah SS2 is freaky (and awesome). But for the real 'omg cool' shock, play the original System Shock and think:
This game came out the same year as the original Doom. (1994)
Then, as you fly around, use night vision, crawl around on your stomach, jump, walk up ramps, listen to dozens of voice logs, use cameras in the back of your head, activate personal shields, get ambushed repeatedly by a stuttering evil computer, use rocket boosted roller skates, look up and down, crouch, shoot out lights and computer monitors, solve story based puzzles, experience an actual story, hack into computer mainframes and fight watchdog programs, rewire keypads, and lean around corners, marvel that Doom did so much better!
Thief: The Dark Project can get pretty freaky-deaky. The Return to the Cathedral was pretty frightening: the evil Haunts and zombies and ghosts infesting everywhere. That was a damn fine game.
RIP Looking Glass!