The
craigslist rental housing game, where posters try to find the best tenant for their apartment/home, viewers try to find the best housing arrangement, scammers try to scam, and weirdos try to do unpredictable weird stuff. If you're using craigslist to look for rental housing and you don't realize it's a game, then arguably you're already losing.

SPIDERS! 
The spiders in SS2 are
terrifying, and I'm not in the least bit arachnophobic IRL.
There are a bunch of good mods to upgrade the graphics. Also a good
spoiler-free guide if you haven't seen it yet.
EDIT:
My only real problem with System Shock 2 so far is that hacking is chance-based. I hate chance-based game mechanics.
Hacking in the first game was far superior: either some logic puzzles or flying around in Cyberspace, which was a lot of fun. The point though was that if you failed, it was your own damn fault, not just the RNG being a dick.
I liked the chance-based hacking etc., although I was generally risk averse. If things looked iffy, I usually reattempted the hack rather than continue.
It's probably less of an issue if the RNG is something high-quality like the
Mersenne twister, but I have no idea what SS2 uses. It might just be something from the C standard library.
EDIT 2: That SS2 and Deus Ex still blow people away today just shows how the high system requirements of many recent games are not strictly necessary to have a superb game. The fundamentals -- story, gameplay, writing, sound, VA, level design, etc. -- still matter above all else. (Granted, SS2/DX might well have been demanding when they were released.)