I'll throw in my 2 cents re: ROTJ:
(So I don't have to type it every sentence, everything I write is of course my opinion. Nothing is presented as fact).
It's not a good movie. Not terrible, but certainly not good. The only enjoyment I derive out of it is 1) from nostalgia- growing up in the 80s and 90s, SW was my favorite, ROTJ was second, and ESB was third. 2) It wraps up the story of the adventures of Luke Skywalker and his pals, characters I love.
There's a lot I could write, but I'm going to leave a lot of stuff out that has already been mentioned by other posters.
My main gripe is I generally don't like the tone of most of the movie (other than the Luke/Vader/Emperor scenes). There's too much for me to write here, so I'll get back to this point in a later post.
In addition to problems with tone, the movie has 3 scenes that are simply bad. While a bad scene doesn't make or break a movie, having 3 of them hurts the movie significantly.
1) The droid torture scene.
I think this is just awful. Cringeworthy. Boring, bad for pacing, bad dialogue, annoying robot with terrible voice. Droids are getting tortured... and it's played for laughs? I don't really get what the scene is trying to achieve. Threepio and R2 are now owned by Jabba, got it. Don't need an explanation that Threepio will be an interpreter and Artoo will work on the sail barge. Whatever they're doing at Jabba's, they're doing because he owns them. Thank you, I understand.
2) Ben/Luke scene on Dagobah.
Boring, flat. If you zoom in on the blu-ray, you can actually see Alec Guinness reading directly from his script. Characters are just sitting on logs (hmm, boring, emotionless characters spouting expository dialogue while sitting. Brilliant foreshadowing of what was to come in the PT!).
The biggest problem with this scene is how Ben defends his lie about Vader. He's completely emotionless, as if it his lie was no big deal. (Reminds me a lot of Lucas in a way, how he unemotionally explains his revisionist history, "Actually, Greedo was always meant to shoot first." "Star Wars has always been the story of the tragedy of Darth Vader.").
"Luke, you're going to find that many of the truths we cling to depend greatly on our own point of view." OK, Ben... other than the Vader/Anakin situation, could you please back up this statement with another example of this? 'Cause it sounds like you're just a lying asshole and full of shit.
What a missed opportunity! How about having a scene where Ben, distraught, perhaps on the verge of tears, confesses to Luke and says something like, "Luke, I'm sorry I lied to you. You were so young and I knew the truth would devastate you, so I lied to protect you. Will you forgive me?" They could have constructed an emotional scene and have made the audience actually FEEL something. But they went the completely sterile route.
3) Luke/Leia scene on Endor
Ugh. Bad dialogue, bad acting. "I didn't know... but somehow... I've ALWAYS known." Whuck?
So in addition to many of the negatives people have already mentioned (some I agree with, some I don't), I think those 3 scenes are simply terrible, and hurt the movie greatly.
I don't hate the Ewoks. I mean, I don't LOVE them, but they're ok. Well, they're too damn silly, but I guess I don't mind the CONCEPT of them. They're not good, but the Ewoks themselves do not ruin the movie for me. In fact I sometimes find myself defending them when people say, "there's no way the Ewoks could defeat the Empire!" They didn't... nor did they have to. They simply distracted some troops while experienced rebel commandos blew up a bunker.
I also hate the briefing scene. Bingowings covered that pretty well. "Hey, anyone else want to be a general?" "Hey Luke! We don't mind you at all barging into our super important meeting!"
Re: what AntcuFaalb said a few posts back, where, I'm paraphrasing, he said something like he looks forward to seeing Salacious B. Crumb more than he does Vader killing the Emperor. In some ways, I actually agree with this, in the sense that the whole Vader redemption is, IMO, kind of ridiculous and silly. Luke thinks he can be redeemed because there's still good in him. Why, exactly, does he think that? That's never answered. In addition, Vader is a boring weakling throughout the movie.
So those are some reasons why I don't like ROTJ. I'll get back to tone later.
SW - a perfect 10/10
ESB - 9/10
ROTJ - 4.5/10