I've been playing Fallout 3 a lot lately, and calling it a FPS is, in my opinion, a bit of a fallacy. It had FPS elements, yes, but it's not anything like what I would imagine most people would expect in an FPS. It actually threw me off plenty of times. Headshotting something in an FPS almost always results in a kill, which is far from the case in Fallout. Fallout, despite the default first person perspective, has never really been a shooter of any sort. It's just not built that way, and I'm glad it isn't. Though I will say that compared to oblivion, fallout at least does give you more damage if you hit in certain areas, such as the head. Still, I'd say that's a cursory nod at best. Even if I am getting chased by a super mutant behemoth, I'd think that if I plug him in the face with a shotgun it should take off more than like 2 dashes of his health. I imagine that's why some fps fans would hate fallout 3.
For the record, I do and always have thought that Fallout 3 was a brilliantly done game. Easily one of my favorites ever.