Maybe not a FPS but a third person shooter adventure, action horror game called Shadow Man. It seems not many people know of the game unfortunately but GameSpot seems to still have a good community of players. Made back in 1999 it's not abandonware (not like it will ever be at 700+MB) but still sold at CDAccess. Also it's requirements are low and it works on XP (even in Win95). I reckon it's one of my favourite games with a great story line, graphics and sound effects. Pretty weird that it comes on N64 considering it is mature for "violence, gore, profanity, implied sexual situations and psychological scares."
Freaky music too
It even has Jack the Ripper starring in it!