Requiem: Avenging Angel
 

Ok, maybe noone plays this because of the DirectX-bug, but it was still the one and only FPS (appart from Doom2) what I've enjoyed to play.

Also maybe you find strange asking for solutions in a shooter-game, but I confess I could never ever beat the bosses! So if you have any strategy against them, tell it to me. Especially against the endgame boss, as for that I rly have no idea whatsoever.