I'm going to go on record and say that the Tragedy of George Lucas started in ROTJ. Watching it for the first time in a while a few years ago, the Gonk Torture scene[1] was where my switch flipped. That scene is just a callout to the looped animatronics in the line at Star Tours --- does bad looped robotic torture add anything, or did Lucas put it in because nobody would tell him no. I think ROTJ is also where Lucas started becoming dependent on chroma key (although he had used it before). Some of the chrome keyed scenes are groundbreaking effects wise, and that's neat, but it takes away from immersion.
The prequel trilogy has so many scenes that feel sterile because the actors are clearly separated from the backdrop. It's hard to feel like the actors are in a desert wasteland when they don't even look warm.