The reason ROTJ get’s flack is because of the Ewoks who kill the pacing and diminish the Empire due to them being a big reason in why they fall. Also Leia being Luke’s sister is universe shrinking but with the “I’ve always known” line makes their whole history almost nauseating. Furthermore they just made them siblings in order to resolve the love triangle so it doesn’t feel like a natural part of the story but rather a cop out. Luke’s temptation should have been a lot more than Palpatine saying “Your friends are going to die” a million and one times. And as shitty as SKB was Death Star 2.0 was a more overt rehash than that one. Lastly and most importantly imo the destruction of the Death Star and the loss of Vader and Palpatine shouldn’t have been the end of the war. With all the other ships, troops and Imperial Officers the war would have realistically gone on for years to come. But all that is thrown out of the window for a phony fairy tale ending.

EDIT:

Not saying it’s a bad film; it’s pretty good but it was a bad way to end the trilogy. Especially if it had been the last film in the saga.