It's very uneven. I mean, it's SW so I love it, but once they get to Endor the movie's schizophrenic. The David/Goliath thing Lucas tried to do via Ewoks was a complete failure to me, but everything else (aka Sidious/Vader/Luke) is amazing. The 1st act is also very entertaining and the Yoda/Obi Wan scenes are magical.
I agree with this description. Frankly, a lot of it is also shot quite poorly and thus a lot of the action sequences aren't as exciting (though that speeder bike chase is still fantastic), and a lot of the more talky-talky bits aren't as interesting.
The Ewoks themselves are alright, unnecessary sure, and clearly there to sell toys, but they're not as horrible as some make them out to be - they're certainly no Gungans.
I also find the first half of the film to be quite boring, personally. There are some definite stellar moments in there, but for the most part, I find the pacing to be way too slow (don't even get me started on Jabba's house band). In fact, most of the film feels like its all set up for the conclusion. But thankfully that conclusion is stunning.
The space battle is great, though honestly the least memorable of the trilogy for me (I'm also not a big fan of the concept of a new Death Star), the Endor stuff definitely picks up towards the end. But ultimately, the Vader/Luke/Emperor stuff is what seals the deal for me. It's so well done that it makes me forgive most of the film's flaws and makes me love it.
I find this to be easily the worst of the three. It's the most flawed, the worst paced and often the most boring. But some of Star Wars's greatest moments are in there, that's for sure. And it provides an extremely satisfying conclusion to the saga, so for that, it will always stay an awesome film in my book.