I think one of the things that bugs a lot of people is how Palpatine's survival undermines the characters' sacrifices and triumphs in the previous movies. It bugs me, too. But in fairness to the writers and directors, would it have been possible to create a sequel to the original trilogy which didn't, in some way or form, undermine the achievements and accomplishments of the previous two trilogies?
The obvious answer from EU fans is the "Thrawn Trilogy", but even there, regardless of what you think of the quality of the writing, it would mean the final victory in ROTJ wasn't final, Anakin Skywalker didn't restore peace to the galaxy, and so on. In addition, any story about how the New Republic isn't so great after all simply winds up retreading the same ground as the prequels.
I think if you look at a lot of the best-loved SF/Fantasy sequels, usually they've been follow ups to small-scale, low-stakes, character-driven stories rather than end-of-the-universe "Chosen One" tales:
Aliens--Original focused on one alien, one crew, one ship, leaving room for expansion and escalation.
Wrath of Khan--Star Trek was built around a serialized, monster/villain-of-the-week format, and the ST II's villain's goals are very specific to the character.
Dark Knight Returns--Comic books in general have a certain degree of recursiveness built into the format--you know that no matter how many times Batman defeats the Joker, the Joker will always escape again--so as with Star Trek, it's more of a defeat the villain of the week format rather than "save the world" story.
Mad Max (either II or Fury Road, depending on your tastes)--Again, the focus is on the survival of one specific group of people, not the entire planet.
*Borderline Case*
Terminator 2--This one walks the line, as John Connor is a kind of a save-the-world "Chosen One" figure, but I'd argue T2 works because the main character is his mom, Sarah Connor, and her survival/victory in T1 is never negated or retconned. I think this is also why later sequels have struggled.
*Exception that Proves the Rule?*
Lord of the Rings--As a sequel to the Hobbit, it again expands on an (apparently) small-scale adventure. It's interesting to also consider LotR as a "sequel" to the Silmarillion, even though that was published after LotR and indeed after the death of JRR Tolkien himself, where the stakes are actually much smaller, and it does appear to undermine the victory over Morgoth. However, here the overall theme of Tolkien's works is one of the gradual fading/decline of magic and its replacement by our very mundane and ordinary world. It's notable that Tolkien tried and quickly gave up any attempt to write a sequel to LotR, noting it would only be about how people get bored with goodness, and thus wasn't worth writing about.
In that sense, I think it's also very notable that there has been a much more positive reaction to the Mandalorian, which is, yep, you guessed it, small-scale and character-driven.
TL;DR I don't think ANY sequel series would have been rewarding to watch, as you're trying to follow up the kind of story which by its very nature doesn't lend itself to sequels.
