My two cents:
1. Trailblazing as the effects and digital cameras were, the makers should have waited a bit longer. The blu-rays don't look as good as the movies could have been.
2. TPM has Anakin being rather more of a MarySue trope than Rey was. But the prequels are easy to forget...
3. The movies plod their plot so incessantly that were they worth doing? There's little emotional depth to the characters - never mind those whiz-bang action sequences - that, if the actors are being wooden, they're all acquitted from the get-go. Especially as all the actors have done stellar work in couintless other films, the prequels just feel so out of sync. Having names like "General Whiny Grievance" and "Black Friday Maul-er" and "Count D. Doodoo" and "Queen Senator Amidalek" and "Quack Boy Djinn" and so on and so on certainly didn't help... oh wait, did I just make a mock? (Yup, I feel sorry for the talent involved...)
4. It also bugs me that the prequels have much better technology than the original trilogy. Can attrition really explain the gulf between the prequels and original trilogy? If that was even the intent, noting point number six below as the preemptive rebuttal to this point?
5. Added on that, the movies themselves have zero continuity. Red Letter Media, Everything Wrong With ___, etc, nail it at every turn - not that one needs to see those to pick up on a number of issues... they just utilize more time and resources in doing so in order to make more entertaining productions.
6. You know there's a huge blunder when storyboarding the prequel trilogy's chapters when Darth Maul - by far the best thing about the prequel trilogy - is dispatched only after 12 minutes of screen time and in the first of the three entries, no less! Yet in later movies the shiny guards with the dual-blade purple stun sticks are trying to suggest "Yo, audience, if we weren't this myopic we would have had Maul back and with his best bud for double the double saber action. Sorry about that! Here, buy some toys - they look great next to Windu's purple saber."
7. Sand. Not only does it get into places we daren't ever say in a family movie as Anakin talks to Amidala about places he never wants to get busy with her at, it's used to make the microchips to produce the soon-to-be-dated special effects.
Now, the prequels certainly had potential in universe expanding and in some ways it's not unappreciated, but given the clunky execution with a lot of that dialogue, "quantity over quality" with pointless lightsaber and space dogfight scenes, exposition told with precious little shown, was the exploration of the universe really necessary? Or even wanted? A coughing robot that can twirl his egg beater arms to whisk out four light sabers, what with it getting dispatched quickly afterward and all, wasn't a spectacle people were clamoring over. Did toy sales help?
Especially when the "special edition remastering" was done largely to appease the prequels, with those changes only adding to the problems. Even good decisions like getting
Iain MacDiarmid into TESB has him spouting off so much dialogue that the end result is counterintuitive. If they chopped half of what he recited for the new footage and took out the big hint of Luke = Anakin's kid, that would have been perfect. (And, yes, some of the changes were worthwhile... sadly, so many weren't...)
In retrospect, even TFA - which has its share of awfulness - still isn't as bad. Mostly due to the characters, and how they get developed (and subverted) in TLJ (thankfully).
I know of the novels and video games, all now decanonized...
