A point that I once heard, and largely agree with, is that Return of the Jedi is a very uneven movie - the rescue from Jabba's Palace and the Sarlacc Pit is thrilling, and the final confrontation is a great ending (particularly the Luke-Vader-Emperor scenes). It's the middle that loses a lot of people, and the prominence of the Ewoks. With that in mind, I suggest a few changes:
Star Wars and The Empire Strikes Back both had very strong senses of three-act structure (you can tell this best in location; Act 1: Tatooine/Hoth, Act 2: Death Star Interior/Dagobah and Bespin during the day, Act 3: Trench Run/Bespin during the night). If we beef up the second act of RotJ, we can recreate that sense (since too much occurs on Endor during Act 3 in OTL's version to draw this same, clear distinction). Similarly, since we're bringing both Han and Lando back, we might as well build a subplot there to inform and reframe our main conflict of Luke and Vader.
That gives us a pretty identical first act: Leia goes to Jabba's Palace to rescue Han, get captured herself, Luke and Lando also arrive to help, and we end up with the battle at the Sarlacc Pit and our heroes reuniting with the Rebel Fleet. Here's where things begin to change, and we mirror ESB rather than Star Wars - Mon Mothma tells us that the Imperial Fleet is doing something, but we need our heroes to find out what it is. Meanwhile, we see Vader meet with the Emperor, but we don't see where it is, the fact that it's a Death Star II being kept as a reveal. Han, Lando, C-3P0, and Chewie go to an Imperial Black Site in the ruins of Alderaan and the Death Star, while Luke, Leia, and R2-D2 go to Dagobah to resume Luke's training, and because Leia says she wants to meet this "Master Jedi" so she can get her own questions answered about why she could "feel" Luke at the end of ESB. Here we get to the heart of our main argument of the film, whether or not redemption is possible, with two "triangles": Luke-Leia-Vader, and Chewie-Han-Lando. Luke and Chewie both believe that the one at issue, Vader/Lando, can be redeemed for their past evils by their current actions, while Han and Leia are skeptical. Luke and Leia visit Yoda, who is still dying, though he gives a different explanation: he is being called back to become one with the Force, as it is time for a new generation to take over. He tells Luke that he has nothing left to teach him, rather than Luke needing no more teaching, because the rest of wisdom is for a person who is in tune with the force to discover. He speaks with Leia in private, where he tells her of her true lineage, and that the force, too, flows through her. He tells her that it binds her to every living thing in the galaxy, her father included. Meanwhile, Han allows himself to trust Lando, and the crew discovers that the Empire has built a second Death Star, it's near the forest planet of Kashyyyk where they use wookie slaves for labor, there's a shield generator on the planet, etc.
Begin Act 3: Luke, Leia, and R2 rejoin the strike team to go onto Kashyyyk, and Luke has the same feeling that he will put the mission in jeopardy because Vaden can sense his presence. Here, though, he jettisons himself in an escape pod after sharing a last hug with Han and Leia, knowing Vader will intercept the pod and capture him, but only after the strike team makes it to the planet surface. Here, things get back on track, as the strike team meets a group of wookie slaves and they lead them to attack the shield generator. Luke comes aboard the Death Star II, starts trying to redeem Vader, meets the Emperor, "Now witness the firepower of this fully armed and operational battle station!" The rebel fleet gets caught in a desperate battle, because the wookies already rose up, there's no last minute saving from the Ewoks when Imperial forces counterattack the rebel strike force, and Luke starts giving in to his anger. Here, we see the value of both redemption and forgiveness; Han tells Lando to get to the Falcon, get up to the space battle and take command. Lando does so, meets up with Wedge and Rogue Squadron, and forms an on-the-fly strategy to go into the Death Star and blow up the reactor from within ("It worked last time, but there's no exhaust port, so we'll just have to go in ourselves!"). Han, Leia, and the rest seem to be in a Bolivian Army ending, but Luke pulls back and forgives Vader, leading to the Emperor shocking Luke. Vader kills the Emperor like OTL, and Lando destroys the Death Star as in OTL. No A-Wing destroying the Super Star Destroyer because here, every victory the rebels win is the result of a positive character choice our heroes make (liberate the wookies - capture the shield generator, trust Lando - destroy the Death Star, forgive Vader - kill the Emperor). Vader dies as in OTL, Luke takes his body, and the Death Star explodes. The tide of the battle in space turns as Imperial ships jump to hyperspace, and we see admirals saying they'll live to fight another day. As Han, Leia, and the rest seem doomed, Han confesses his love for Leia (to which she responds "I know" and the two kiss), and reinforcements led by Luke arrive, driving off the Imperials. That night, they burn Vader's body, have a wookie celebration, and we see Anakin, Obi-Wan, and Yoda looking proudly at Luke and Leia, who both see them.
That, I think, fixes the most-complained about feature (the ewoks and their prominence in the story - even the wookies here will get less screen time) and the biggest structural problem, a weak second act (OTL, they go to Endor very early and have their misadventures there, from the great speeder bike chase to the less-great "C-3P0 is a god" bits). It also gives Han and Lando more to do, since they both fall more into the background here, and gives Leia more agency by giving her an ideological position in opposition to Luke and a character arc of her own.