I personally felt Superman III was more disappointing than this.
I can understand why nearly everyone hates this movie. I'm not saying Superman IV is good. Yes, the giant plot holes and cheaper budget makes it nearly unwatchable, but I personally thought Superman III was much more disappointing IMO.
Superman IV at least has the tone of the movie right and the soundtrack is quite decent. I really liked Nuclear man's theme. The key characters from I and II are here again (Lois, Perry, Lex) and also the Fortress of Solitude and green crystal (which was completely forgotten of in III). Superman IV at least tried to be a comic book movie.
Personally, I really hated Superman III because it had an overbearing generic 80s comedy movie tone. I felt the real disappointment was all the wasted opportunity for part 3. We just got a Richard Pryor meets Superman movie. When I watched it on VHS, I had to remind myself I was watching a Superman movie half the time. When I first watched it, I thought we rented the wrong movie until I saw the Superman III title over a random slapstick opening. Superman III also had a much larger budget and the success of Superman II to springboard off of. And even as a kid, I didn't find Richard Pryor funny at all in this movie. Superman 3 has nearly no relationship to the comics. It almost reminds me of the Star Wars Holiday special where we take a franchise and combine it into whatever is "in" today.