I noticed users have come with a long list of suggestions, and I have several myself; however for the sake of brevity, I’d focus on the most pressing to me: The film’s structure, more specifically that of the third act.
Often it has been brought up how this film’s climax (and that of TPM) feels like a collection of scenes. Indeed this a problem with a great many blockbusters, multiple climaxes playing simultaneously (The Matrix sequels, The Return of the King, Marvel’s nonesense, etc), often with the transitions feeling choppy or non-existing at all.
What comes to the top of my head: Since the most interesting of the three scenes is the Duel, it ought to be emphasized more. Rather than “meanwhile in the Death Star”, Luke has to be looking at the battle as it progresses, perhaps even catching a glimpse of the Falcon being chased by fighters. As it currently stands, all he sees (as does the audience) are tiny ships in the distance, it’s not clear who’s winning or losing. The scene must also be affected by what’s happening on Endor. Luke could very well sense Leia being hurt, an in turn Vader and the Emperor could feel such turmoil in Luke. What about Leia sensing Luke being tortured by the Emperor, would that be too intrusive?