It is agreed upon by many that rotj could've been a better film, but there are still some very powerfull moments in the film, in fact some of my favorites in the trilogy. Besides the fact that fett goes down like a chump, and theres teddy bears instead of wookiees in the ground battle, originally was going to be Kashyyk not endor. The confrontation with vader and the emperor was supposed to be on then named had abbadon, capitol planet world of the empire imperial center (coruscant came from some eu author), in it's very depths so far down their would be lava in the emperors inner sanctum, not the death star II.

luke and leia unknowingly being brother and sister is an old archetype concept and I think lucas took it from greek and roman mythology, notwithstanding that he kept going back and forth over whether or not she should be his sister, or vader his father that is what he finally decided upon.

Luke's story originally was supposed to be 6 films, and was compressed to three. , in the original plan that also left the prequels and the sequels, that is why there were twelve episodes planned. the story that could've taken another 4 films to tell after empire strikes back was compressed to fit one movie.