I actually agree with you, Warner.
Rocky is a legitimate, all-time classic American film.
My minor disagreement with you though, most of the heart that made Rocky go, is gone in II. We know why Rocky II was around, it was the realization that this character from Rocky has the potential to be a franchise...so they hotshotted the title on him. Similarly in the way, say...Nightmare on Elm Street 3 was the realization that it was a franchise and a direction changer or Friday the 13th II. Those are your equivalents to Rocky II. Good movies, but you know why you're there, and they are a changeup from the original films.
III and IV are full on 80's camp, but camp done the right way. Its not poorly done like its winking at you the whole way or laughing at itself, its just taking this story and taking the cheeky concepts from the first two films and really blowing them up. I really dig them as habit-watchers and still find enjoyment in passing by them on a Sunday morning and staying there. If you pass by Rocky IV when channel surfing and "Hearts on Fire" hasn't played yet, its your duty to sit there, watch it, and wait for it.
V is an abomination. It was trying to be campy, but campy like its trying to not just emulate its core concept, but trying to be the late 80's teen angst film, too. Really bad stuff.
Rocky Balboa is the proper ending to the series. Tonally, more in-line with I with the proper sendoff to the character.