Why is ROCKY V More Hated Than ROCKY IV?
The fourth movie is incidentally, the most successful box office wise of the six movies. I mean lets put it this way:
*Out of the six movies Rocky IV feels the most dated because of the Cold War/Soviet Union angle.
*Rocky Balboa perhaps, came across more like a superhero type character having to conquer the big bad comic book like monster (a la Darkseid or Thanos) in Ivan Drago than a regular guy (you can argue that that same happened w/ John McClane in the fourth Die Hard movie). In a way, the Rocky series were already going down the one-dimensional, over-the-top "monster of the week" path w/ Clubber Lang in the third movie. Hell, Rocky IV its really just a glorified MTV music video/propaganda piece when you get right down to it.
*Rocky wouldn't have gotten brain damage in the first place had a rusty, past-his-prime Apollo Creed not been so jingoistic, cocky and stubborn (even Rocky told him that he didn't think that it was that good of an idea to be fighting Drago) to challenge Drago to a fight (thus get literally beaten to death and cause Rocky to challenge Drago himself as means of avenging Apollo's death).