Heck, even ROTJ had some dumb problems with it (not as egregious as the prequels), but making Leia Luke’s sister was problem #1. Making Darth Vader Anakin Skywalker was the other problem. It completely turns Obi-Wan Kenobi into an abject liar.
Ewoks could have been better. This article explains things very well....
http://www.filmthreat.com/features/172/
However, there are a few things about ROTJ I like very much, but it doesn’t save it.
I went through a bunch of it. I hate smarmy critics like the one that wrote that hitpiece on ROTJ with a zillion nitpicks. What has that critic ever created? Let these assholes who are offended by the torture of droids produce their own epic. The first three were all good with ROTJ being the best of the lot IMO.