I loved Rocky 1, liked Rocky 2 and was indifferent to Rocky 3. I had no plans to watch Rocky 4 until one of my friends told me it was their favorite, and I'm glad I watched it! A great installment which resurrects some of the spontanaeity and wackiness of the first film.
With that said, I'm frustrated that it's absolutely impossible to avoid spoilers when purchasing/renting/browsing shows on Amazon Prime. If you're summarizing Rocky 4 for a friend who hasn't seen it, would you reall tell them "Oh yeah! Rocky Four! That's the one where Drago kills Apollo Creed in an exhibition match, and Rocky flies out to to Russia to defeat him in a 15-round match!"
Amazon's tagline spoils the entire movie, it's just the worst thing ever. No part of that should be in the tagline. How about this instead, "Rocky Balboa proudly holds the world heavyweight boxing championship, but a new challenger has stepped forward: Drago, a six-foot-four, 261-pound fighter who has the backing of the Soviet Union."