Long before BioShock was released, there was System Shock. Also created by the hand of Ken Levine (at the now-defunct Looking Glass Studios), the game was one of the first of its kind: a shooter RPG with a sci-fi backdrop and elements of horror. System Shock, tragically, sold very poorly, though in its later years has gained significantly in popularity. Fans have a lot to get excited about today, as a new mod has just been released which adds some much-needed features to the experience.
The "Mouselook mod" comes to us from "Malba Talhan." Though many thought it impossible, he's managed to add support for (you guessed it) mouse look, mouse sensitivity, and configurable keys. Also, ToxicFrog's high-resolution mod is integrated into it, so you can achieve up to 1024x768, with 1280x1024 said to come once the bugs are sussed out.
Mouse look is the biggest addition here; it's known to be the biggest obstacle in the game's learning curve, so now's definitely a better time than ever to give it a shot if you have the means.
Grab the mod at the source.