System shock 2 is a definite play for all gamers who like horror games. It is definitly one of the best concepts ever made for a game, and with the rebirth mod looks very nice.
In my opinion this is by far the most scary game ever since it goes beyond all games in terms of the fear. System shock 2 not only has the monsters, but it has the isolation and the insane individual stories of how events on the ship go wrong. FEAR, Doom 3, Resident evil dont even come close to the feeling I get while I play system shock 2.
Get system shock 2, its legal to download it since no one holds the rights to it anymore.
Ive done lots of horror games, this is one of the only ones that really makes me scared.