I think American Graffitit and Star Wars beg to differ.
The problem is that fans interpreted things differently. Objectively the prequels are still good films, its just they weren't what fans who are now in their 40's and 50's wanted them to be.
Up until the 2012 Disney buyout I was a HUGE Star Wars fan. Im talking about all of the Celebrations(in the US) and $5,000+ of Hasbro/Kenner figures. That series was my life. That being said I have no reservation saying Star Wars fans(particularly the older ones) are some of the most entitled fans out there. The Prequels were never going to be what some fans wanted them to be, honestly, that's for the better. My fear with these new movies is that they are essentially going to be an example of slightly different Star Wars being passed off as new and shiny but largely staying the same. Several rumors up to this point have been confirmed by the trailer, which is a shame because the rumors imply we are essentially getting ANH all over again. I don't want to see that movie, I've seen it hundreds of times before already.
Objectively the prequels are not good films.
This has nothing to do with "they runied Vader" or something dumb like that. The fact of the matter is they are pieces of crap movies.
They are lazily directed, badly written, lack any form of cohesion, the pacing is crap, the characters fall flat and (the last two) rely on green screen to much and just look fake.
They are bad movies. Not bad Star Wars movies just bad movies period.
The Star Wars prequels are textbook examples of how complete creative control can lead to a disaster of a movie. You saying they are objectively good movies is one of the most laughable things I've read here.