Mustafar looked mostly okay. If the prequels had told their story effectively then the effects would be forgivable. There are some really crappy effects in Return of the Jedi but the movie is interesting so it’s okay.
I’d take RotS over RotJ any day, but I realize I’m in the minority here.
Not sure I’d say the same but I think they are closer in quality than most think. RoTJ is just a very mediocre movie at the core with some standout moments.
Visually it is miles ahead of Revenge of the Sith. Your in a forest for half the movie and it’s nice that it actually feels that way!