Forgot this the first time, but:
I liked FEAR. Much more than Half Life 2 or Halo. Possibly because I dind't found the storry that awfull (it wasn't good but not that terrible either) and it's the only FPS where I felt the ennmies gave me a genuine challenge (if you don't spam slomow too much, that is).
Haven't tried the 2 or the 3, but frankly they look awfull AND unlovable.
@V I don't know the level design and the main campain storry have to count as 'sucky' for some. And Nortoooon Maaaapes.