Doesn't S.T.A.L.K.E.R. incorporate elements of Rpg into it?
Do'h, been trying to think of my other "go to" game for why fps/rgp's have so far been mostly horrible failures.
Both Stalker, and Bioshock do the whole "character levels up, significantly" thing, but enemies, do not really at all.
Stalker was the worst, the first 2-3 guns you get are falsely and stupidly inaccurate, get to the next area, first gun you get is pinpoint accurate, a gun within the first 90mins of the game, is good enough to headshot anyone for the entire game. Likewise the artefacts made you almost invunerable within a couple hours playtime, giving the rest of the game no feel to it. Bioshocks the same, 2 hours in, invunerable, lose any real sense of caring about your superhuman self compared to the mere mortals you're fighting.
Stalker, was supposed to be a massive RPG though, which ran out of time, money and man power so cut tonnes of the game out, thats understandable but still badly done. Bioshock, was just badly thought out.
Too many FPS/RGP games are focusing primarily on the character scaling up through the game, while enemies don't, which is where they are tending to fail heavily compared to a normal RPG which do one of two things, enemies of various levels and you can only take on some after you get to a certain level of ability. Others where enemies get harder as you get stronger.