SS2 will grab you by the throat and send you flying through a bizarre, almost surrealistic cyberpunk horror story.
The story, which unfolds at a creeping yet pitch perfect pace, is one of the greatest told in video games. It starts off relatively simple: You are an operative aboard the USS Von Braun. You are awoken from Cryosleep with a new cybernetic module wired into your eyes and brain. A woman talks to you through a speaker, apparently the only other survivor. You soon learn of "The Many," mutated humans infected by a strange worm, and their intent to kill you and the other survivor, who leads you through the ship. Despite the simplistic set up, the games mysteries unfold and expand as you progress. There's a twist to the game, but I shouldn't spoil it, as its one of the greatest you'll ever experience, and let me just say that SHODAN is named the best villain in video games for a reason. You don't have to know the plot of the first game to be able to get SS2, they sum up the basics of it in the opening cinematic.
The game is weird, to say the least. From The Many's chilling cries and animation (As well as their looks, think John Carpenters "The Thing" mixed in with The Borg.) to the bizarre looks of humans and everyday objects. To be fair, the latter element is because of some EXTREMELY dated graphics technology (Dated even for 1999) but in a way I like how bizarre and unreal humans and objects look, because it gives the game an even more bizarre and unrealistic tinge. The game is scary, from the aforementioned atmosphere and freaky monsters, to some genuine shocks and startles. You will dread every corner, ghosts will appear at random and even if you think you aren't afraid of ghosts, they almost always take you by surprise, although they are surprisingly important to finding clues in the game.
It's really hard to continue describing the game. It really must be experienced first hand, there is no other game like it and there never will be another. Check this out! The only real negatives I have lie in the fact that the games engine is bugged beyond all repair, and will barely run on any OS besides Windows 98 unless you download bucket loads of patches, mods, and turn off HyperThreading or DualCore processing, which I doubt many people will want to do just for one game. If you are willing to tweak a few settings though, or if you have a Win 98 computer lying around somewhere, Check out System Shock 2. It is simply put, a Master piece.