And I thought the Jabba scene dragged on too long too. But recently I'm thinking that it allows us to have some badly-needed footage of all the good guys working together. Think about it. Luke had spent most of the last movie on his own with Yoda and R2 (not that that's bad, but Yoda was a new character at that point, not an established one) while the other main characters got to spend time with each other, developing the relationships they began in the first movie. And then, it wouldn't be much longer before Luke was gone on his own again with Vader and the Emperor until the very end. Luke really becomes the loner character of the big three in the sequels. And it's the only time getting to see Lando fight alongside Luke and Han since, almost immediately after this point, he's doing his own thing for the rest of the movie. While it's definitely important and finally gives his character a chance to shine, it completely destroys any kind of intercharacter-relationship development that could have been going on. And his character definitely needed that, especially with Han, after the events of the previous movie. It warmed my heart to see them embrace at the end montage and their joking during the passoff of the Falcon, but so much more could have been done with that. It really irked me that Han just accepted Lando's help without so much as a question. At least some banter about Lando's betrayal would have been nice.
And of course, Jedi contains one of the few, really big plot holes in the original trilogy: C-3PO as a storyteller. While I enjoy it because it's interesting, it completely contradicts his claim in the first movie that he's not an interesting storyteller... unless he's being modest. Or at some point during the trilogy, Luke thought it would be cool to install a storytelling chip in his droid to keep him from being so stuffy and annoying (just kidding, I love 3PO... except in the PT where he really is the most annoying character... more so than Jar-Jar... "I'm beside myself," indeed!)