I think the ROTJ has the reputation for worst of the OT (which is like being the skinny one in the cast of Predator) for a couple reasons.
- Han, Leia, and Lando don't have a lot of character development.
- The Ewoks.
All the character development is kind of hogged by the Luke/Vader dynamic. But as Zombie said, that's just SO DAMN GOOD it's hard to fault it the attention it recieves.
Frankly, except a couple moments I think are too silly (trying to trip the AT-ST with a rope) I think the Ewoks are unfairly maligned. When we meet them they want to EAT our heroes. That's not the action of little teddy bears.
As for the climax being repetitive with "Star Wars" I guess I can see that bothering someone, but really it's so much larger it's never bothered me at all.
"Star Wars": A small group of plucky rebels with our main hero among them go against the Death Star and are fought by the villain!!
"ROTJ": A huge fleet of rebels with Lando among them go against the Death Star, while at the same time a massive land battle is going on with Han and Leia, and at the same time a lightsaber battle/psychological warfare is going on inside the same Death Star between the main hero, his father, and the dark sorcerer who rules the Universe!