Jedi was just a bunch of muppets.
The final chapter to the Star Wars Trilogy was a triumphant conclusion to the story that began full of energy in "Star Wars" and strengthened in "The Empire Strikes Back", full of eye-popping special effects. It was also probably the weakest effort in the trilogy, being more of a merchandising engine than anything else. Other than new footage in Jabba's palace with a new song-and-dance routine and CGI replacing the Max Rebo muppet (with the visible wire under his trunk), not much else has changed (yes, that's why I paid five bucks to see a Star Wars movie-- to enjoy the new musical number!).
So what went wrong with ROTJ? It was basically a dumbed-down version of SW that maxxed out all the merchandising possibilities it could. The cute cuddly Ewoks are the prime example. They bring unfunny physical comedy to an otherwise serious (well, even that's debatable) movie, they look like exactly what they are (kids in furry suits), they sang that awful song at the end (at least they took it out for the Special Edition), and they unconvincingly beat the crap out of a whole platoon of Stormtroopers with sticks and stones (challenge the status quo when you watch ROTJ:SE-- CHEER when the ONE Ewok dies during the battle). There were muppets all over the goddamn place, from Jabba himself to Salacious Crumb (the annoying dog-thing at Jabba's side) to Max Rebo (did I mention the wire attached to his trunk?). The movie is essentially SW with minor modifications: another Death Star to blow up, another energy field to shut down, a Star Destroyer crawling across the screen at the very beginning, etc. This lack of innovation is also apparent in the characters. C3P0 really has nothing to do in this movie other than being the butt of jokes and getting in the way. Boba Fett, the cool bounty hunter introduced in TESB, is sacrificed for an insipid attempt at humor-- he falls into Sarlaac pit and the beast burps. Yes, Boba Fett killed for a cheap laugh. The acting leaves much to be desired-- Harrison Ford just wants to get out of his contract, Carrie Fisher has a coke habit, and their scenes together look forced (Leia and Solo are supposed to be in love, but they certainly don't show it). Another 'dumbing down' would be the spiritual metaphor of Obi-Wan's voice in Luke's head-- however in ROTJ, it is literalized and a glow-in-the-dark Obi-Wan actually walks over and sits down next to Luke. Also, some of the worst dialogue in the trilogy is found in ROTJ: "I have a bad feeling about this" is spoken at Jabba's palace and on Endor, and the trio "I gotta get you outta here", "We gotta get outta here", and "Let's get outta here" rear their ugly heads. Finally, "Luke's my brother." 'Nuff said.