Let me first say im also a fan of the original two movies. Greatness.
There are a ton of problems with the prequals but heres the biggest, imho: the original two (new hope and empire) followed a common thread, had a common plot. You can distill it in whatever way suits you but it was essentially a space soap opera set to the themes of meiji era japan. That is the era tha saw the end of the samurai and the shogun rule and all the entire system of governance commerce etc etc it was entire cultural revolution.
The jedi were simply “samurai” and the force was “ki” or whatever other eastern religious energy force you want to substitute. He wove in themes of master/student (obi wan/luke) from eastern martial arts tradition, the lost student (vader) seeking to kill his former “good” master, the redemption of the master by training a new “good” apprentice (remember in a new hope there was no emperor) on on it goes, but you get the point.
the problem with the everything done after empire was that it lost that thread. He didnt progress the story and lost any hope of continuity with his own themes. The prequels did NOTHING to show us the good student turning evil and gave no sense of the students true strength as he slid toward evil. It was all so poorly written and had lost sight of the the prequel story, the student/teacher souring relationship. We got dog shit filled with special effects and we were supposed to be so enthralled that we overlooked the stench.
Redoing the special effects in new hope wasnt offensive... until he had han shoot first. That altered the story and character FOR NO REASON!!! Greedo threatened to take the falcon. Han shot without remorse. Its who he was. A smuggler trying to make a living under a domineering empire. Fuckin greedo shot first my ass. And it looks so awful. The original scene was magic. He leans forwad and “boom”! Greedo dead under the table. Greatness.