My choice would be Serious Sam First Encounter and Serious Sam Second Encounter (Ill cheat and class them as one game since the fusion DLC combined the HD versions together.
Also Quake 2 still stands up today as a very fun action FPS, the fact that the baddies are smaller than other games makes them harder to hit.
Fear 1 is a well balanced FPS with top notch squad AI.
As for story FPS games, ill go for System shock 2, Deus Ex, Theif 1 / 2 and the Half Life series. Morrowind is my favorite RPG / FPS, its a shame that the modern examples of Bioware's and Bethesda's games dont stand up to their previous PC exclusives, but thats the changing times where WRPGs have very little RPG, but are something more like a open world sandbox game like GTA but in FPS form.
