It's the worst of all of them.
ESB was originally the mid-point of a nine-film saga. Then GL decided to cut out the last three, and ESB had suddenly become the penultimate film of merely six, and its open ending did NOT suit a transition into a finale where, staggeringly strangley seeing that the Empire is at full pelt at ESB, by the end of the film the Empire is apparently desttroyed.
The start with Jabba's palace- fine. The final Luke.Vader confrontation? Fine- but the Palace bit was inevitable, and the Luke bit would have been there at the end of the original Episode IX anyway.
Everything else is a shambles. The Solo/Leia romance totally falls apart; the magic is gone and Solo has a poor role in the film. Leia is bumped up to being Luke's sister, almost as a convenience as she was the only female now available to do so. The originally planned Wookie fight becomes an Ewok fight, and utterly crass it is too, GL's attempt to make a Vietnam allegory ruined by the sheer cretinous feleing of the situation (GL muchly improves the situation in TPM, whee the plucky underdog Gungans are actually losing the battle) as the apparently unstoppable Empire is beaten by a tribe of teddy bears.
Likewise, for some reason, the entire Imperial fleet cannot seem to overwhelm the Rebels, which makes me wonder why theny ever evacuated from Hoth; in early films it is VERY clear that the Rebels, whilst well-equipped, are far too small for grand battle. ROTJ makes it look like that they should have just attacked the Imperial fleet from the start; looks like they would have won.
And finally, the continuous plot changes and script re-writes destroyed the ending., The ending is MEANT to be that Luke convinces Anakin to kill the Emperor, Balance is restored and the good guys win.
But they forgot to show the change that killing the Emperor meant
Because Luke was totally irrelevant to final victory- the Rebels won that battle anyway, and both Vader and the Emperor would have died. From the events presented by the film, all Luke did was go to Endor, get captured, and then escape. Without any other consequence to his actions in the grander scheme of things, that plot was a TOTAL waste of time; he may as well have just not gone. Ok, he got to see his Dad, but so what? He was on a quest to defeat evil, not visit relatives.
In many early plot versions killing the Emperor is clearly shown as the catalyst of victory. This is not so in the final version- it simply got forgotten in the excitement of it all, especially when the Emperor was moved from the Imperial homeworld to the new Death Star (the Death Star itself, btw, is another example of ROTJ's failing- simply re-using a plot point like that. It's not as if this was a tv series of 200 episodes; there had only been two films and surely something else could have been thought of).
Oh, I know people SPECULATE that if the Emperor had not died, this would have happened and that would have happened and so the Rebels would have lost. But:
a. We shouldn't have to SPECULATE on something so important- it should have been told to or shown to us, directly, on-screen. Killing the Emperor should have been directly shown to make a difference.
b. Nearly all these theories assign powers to the Emperor that we have no evidence for. It seems clear to me that considerably before his death by Vader's hands, his plan had already failed, the Rebels were going to win, and he would have died.
This major flaw destroys the central plot of the whole enterprise.
The dialogue is poorer, the plot is improvised, the main interesting relationship of the trilogy is diminished, and the central plot arc trips over itself. ROTJ is beset by massive problems that make the problems of TPM and AOTC look small fry, by a long margin.