Why can't there be more games like this?  System Shock 2 is a one-of-a-kind Sci-Fi/Horror game that is a mix between a stealth action game and an RPG.  It defies conventional definitions for games, and that is why I doubt I will ever play another one like it.  I have played some creepy games before (e.g. "Thief", "Arx Fatalis"), but I have never played one before that hit me this hard with a combination of atmosphere and storyline.  You can have nightmares about this game, thanks to its disturbing imagery, dark storyline, and eerie sounds.