(my first post! woot)
Ewoks, sure. They could have been toned back a smidge or two.
I think that the film suffers because Empire was SO good. It's like following up "Close Encounters of the Third Kind" with "Morons from Outer Space." OK, that's a bit harsh. =)
As any OOT fan probably does, I have a little laundry list of things that bug me about Jedi. Similar to most people's, I would bet.
* Just last film, the imperial troopers had seemed bad-ass, like something to be reckoned with. Here they get their asses handed to them by teddy bears. Why do they wear armor anyway? It repels neither blaster shots, nor rocks nor wooden arrows. I think this could have been fixed just by having a lot more Ewoks die in the battle. But then it wouldn't have been so frothy silly and kid-friendly, which it was obviously intended to be, probably to offset just how dang dark the Luke / Vader / Palpatine angle was getting.
* Han. After being so cocksure and generally awesome in the prior films, he gets weak and bland as a character. The script not giving Ford anything to work with? His complete disinterest or dislike for the material? I don't know. He just wasn't nearly as fun to watch as he was in the prior films.
* The space battle was unsatisfying compared to the Yavin Death Star battle, or the chase through the Asteroid field. I think it was just cut so fast, with no real ability to feel like you were in the battle.
Something that bugs me upon every viewing is that the Jabba sequence is just too convoluted. Everybody had to have a part. Would Luke really have given up R2 and 3P0 if Jabba had accepted the offer? I know we had to have Luke in it to show him off as a fully armed and operational jedi, but, since ESB ended with Chewie and Lando heading off looking for Han, they should have been the ones to rescue him. (Then, Lando dying at the end, if he had done so, would have had way more impact.) But then the Erol Flynn epic battle on the skiffs wouldn't have worked out the way they did, and, other than the fact that it seems like Luke is just bopping people with a balsa wood stick rather than a light saber (no flying limbs), it is a fun battle. Best moment -- Lando getting really panicky as Han aims a blaster at him.
But there is a lot to like about the film. The first speeder chase for example. The absence of music makes it a lot more tense. And I think Carrie Fisher actually did a reasonably good job with Leia in my opinion .. her scenes don't bum me out like Harrison Ford's do. (Despite some script dumbness. "I know .. somehow I've always known." Wut?)
And the Luke and Vader interaction ... really, very good. (Yes, I always wondered what would happen .. if he had 'gone to the dark side' as he was being encouraged and killed Vader, what then? "OK, that's done; now that I'm bad for committing patricide, I'm going to go kill my friends, since there isn't a Jedi temple full of younglings to slaughter." But the Last Temptation of Luke is the heart of the film, it's darker than people give the film credit for being, and it really is quite emotional for me. (When he finally gets furious and goes after Vader in earnest ... wow.)
And on the silly side, it really is fun when Chewie commandeers the AT-ST, or when Wicket whooshes off on the speeder bike. (I know some people hate that, but it tickles me greatly.)
I think what always strikes me as I watch the film is that not that it's childish. It's that it's such a mixture of the dark and adult, mixed with the childish and silly. A lot of what happens on 'the sentry moon' is just plain silly. The muppets in Jabba's place are goofy. (And way more so with "Jedi Rocks," but, that's the SE ... ) But then you have Leia in chains in her slave bikini (sproing! I wonder how many nascant BDSM fans were formed by those scenes), apparent tentacle rape or fingering by Jabba, Oola in a fishnet strippers outfit, Luke screaming for hours as Palpatine zaps him over and over .. some extremely intense stuff.
I watched it again recently with my wife, who is much more a trekkie than a star wars fan, and my 8 year old daughter. They both laughed at the silly parts, got tense at the tense parst, and enjoyed it a lot, and, in comparision to the PT, it really isn't bad at all. That's not meant as the faint praise it sounds like -- my opinion of it is higher than it used to be.