In the last Fallout, ferals seemed more intelligent, more 'aware' of themselves and the world, more like any other kind of semi-competent monster in the game- they might have lost their humanity, but they could still be a dangerous opponent if you didn't watch yourself. In F4, Bethesda apparently put all those hours watching the Walking Dead TV show to good use, and have zombified them. Now they are totally brain dead, just laying around like a corpse most of the time until they sense you near, then they slowly get up and akwardly shamble towards you like a classic Day of the Dead zombie. They eventually pick up speed during their attacks, but they're so clumsy they usually fall over themselves after lunging at you. I find myself missing the F3 ferals.
While F3 ferals were kind of depicted a bit cartoonishly, all skeleton and gristle, at least the art was fairly good, and they could definitely look frightening as their slavering jaws closed in towards your face in VATS... they looked- quite animated. I don't think the crappy ghoul artwork in F4 even has any facial animations that I've noticed, the poorly-drawn unmoving ghoul faces always have the same muddy, low-res, awfully textured look on them no matter what is happening. While the world in general is much better looking in F4, the monster art seems to have gone way down hill- on most everything.