The Ewoks were over-used and certainly over-marketed, but they didn't ruin the movie in and of themselves. Return of the Jedi was the first Star Wars movie where spectacle started to overwhelm plot. It's the movie where the effects became more important than anything else. It's also the point at which Lucas seems to begin to believe his own press.
I hear this a lot, and I genuinely have no idea what it means. The whole "Ewoks were a cynical attempt to cash in by making plush toys" canard continues to be as silly as ever (anybody who thinks the Wookiees would have been less marketed had the film involved them instead of Ewoks is delusional), and I don't really see where the effects are overwhelming everything else. Story is always front and center in ROTJ; the plot is always crystal clear and easy to follow. The notion that somehow the film should have had less special effects in it is pretty silly, really; no Star Wars fan would have accepted a movie that didn't end with a titanic space battle, for instance. I've never understood this objection.
That problem became much more evident with the special edition re-releases in 1997 when George Lucas not only re-worked the special effects largely unnecessarily but also tweaked some plot points to the annoyance of many long time fans. This set the pattern for the next 10 years and the tweaking continued and special effects came to dominate even more.
What plot points were tweaked in the Special Editions? I don't remember the plots unfolding in any way other than they'd ever unfolded before. You can claim that Lucas tweaked a couple of character moments (although I've never believed that the whole "Han shot first!" thing represented an emasculation of Han Solo anyway), but not plot. The stories are still the same.
The culmination was of course Star Wars Episode III: The Revenge of the Sith where we are subjected to an opening sequence which is both breathtaking in its CGI sophistication and completely impossible for the brain to actually follow. By this stage special effects seemed to have become a reason by themselves with no plot justification needed.
And here's a shibboleth that I've heard an awful lot over the last couple of years, and to be honest, I find it totally silly.
First off, I'm thinking of a movie that started with a long battle sequence that's so gigantic and filled with mayhem and destruction that it's "impossible for the brain to follow", and that sequence is uniformly hailed as filmmaking genius. I'm referring to Saving Private Ryan, of course. The Sith battle is, I think, equally ambitious.
The larger problem I have with this statement is that, unless you're afflicted with some kind of vision problem or mental malady, it just isn't true. Seriously, if you couldn't follow the opening space battle in Sith, I accuse you of just not trying very hard. Consider: I get up for work at 6:00 am, and I worked a full shift on the day that ended with me going to the theater to see Sith at a midnight showing. So, when the lights dimmed and the movie started, I'd been up for over eighteen hours, and I was able to follow that battle scene just fine.
It's because Lucas knew what he was doing. I know, we don't like to grant that anymore; our standard narrative now is that George Lucas is a bumbling twit who only manages to sporadically bumble into making something good by virtue of his accidental hiring of quality people. But for all the mayhem and madness that explodes across the screen in that space battle, Lucas specifically takes a large number of measures to make sure we can follow things.
First, there's a long tracking shot as we follow the two Jedi fighters into the battle, first following them over the hull of a Republic cruiser before they drop into the battle itself. Thus Lucas gives us about thirty seconds to look at these two ships and register them in our brains, which also helps when it turns out that with all the CGI hell breaking loose, those two Jedi fighters are the only ships of that type in the entire battle. They're patterned on TIE fighters, so they're familiar-looking to us on that score as well, and they're also the only ships in the entire battle whose thrusters fire blue flame instead of red. The action constantly brings us back to these two ships, focusing us not on the battle itself but on Anakin and Obi Wan's progress through the battle.
Maybe I'm speaking too strongly here, but the idea of any experienced film-goer, especially in this day and age of massive special effects battles throwing up their hands at Revenge of the Sith and yelping "I can't follow this!" doesn't wash. If you can follow any of the large battles in the Lord of the Rings movies (especially Helm's Deep, which takes place at night in rain), you have no excuse for not being able to follow Sith. I suspect people who claim otherwise of being deliberately obtuse in order to bitch about something in Star Wars.
If that wasn't bad enough Lucas grew increasingly insistent that the 6 part Star Wars saga we now have is what he envisaged from the beginning. Never mind plenty of documentary evidence that at one point a sequel trilogy was floated. Never mind the fact it's perfectly obvious that Leia was not Luke's sister in the original Star Wars movie. Never mind that the prequel trilogy does not mesh well with the original trilogy even after all the tinkering.
One bad assertion after another. I know that everybody is totally convinced that Lucas's "only six movies were intended" stance is revisionism, but the man said as much back in 1979, for God's sake: the whole idea was originally for six movies, with the notion of a "sequel trilogy" floated after the fact. (The recent book The Making of Star Wars reinforces this point as well: the concept of the series that Lucas finally settled on, after all the drafts he wrote, was of two trilogies: the one with Luke's story, and the one filling in the tale of Kenobi and the genesis of Darth Vader. Now, it didn't become immediately apparent that the overall saga is really Vader's tale until a bit later, but stories do evolve in the mind of their creators as they tell them. Witness Tolkien's oft-cited remark about The Lord of the Rings: "This tale grew in the telling."
It's also far from "perfectly obvious" that Leia was not Luke's sister in the original movie. Sure, Lucas could have gone the other way without contradicting anything in A New Hope, but that's not the same thing, is it? Nothing, not a single thing, in ANH is inconsistent with Luke and Leia later turning out to be brother and sister.
As for the Prequel Trilogy "not meshing well with the Original Trilogy", the writer just drops this assertion out there with no supporting statements at all, so I'm not sure what's bothering him. Maybe it's that there's some stuff from the OT that isn't adequately explained by the PT, but how big a deal is that, really? Do we really need a canonical explanation of why Dagobah seems familiar to Luke in TESB? Or Leia's incredibly vague memories of "her real mother"? (Seems to me that the latter could be explained by Leia's own gifts with The Force, which she's never been trained to use in any concrete way. Surely people with affinities to The Force aren't all skilled in the exact same ways.) If so, that's pretty weak tea – and anyway, how bad is it if the continuities don't line up exactly, anyway? I don't think that the PT had any real obligation to line up exactly with what the OT had to say about the events that took place in that time period, since in the OT we're dealing with the memories people have of terribly stressful times over two decades previous, memories which can be faulty and colored by people's own natural tendencies to inflate the importance of their points-of-view.
I suppose that's it. The rest of the article is just more silliness like that, in which the point constantly gets missed. The writer is apparently annoyed that Star Wars got away from its pulp origins, when anyone who gives a moment's thought to the matter can see that it's pure pulp all the way. I'd only note that just because you didn't have fun at the Prequel Trilogy doesn't imply that they weren't intended to be fun. Just because The Family Guy doesn't make me laugh doesn't give me the right to claim that it's not a comedy show.