The problem is, the prequels could and should have been tons better. The few references to the backstory given in the movies suggest a much more interesting story than what happens in the prequels.
"You fought in the Clone Wars?"
"Yes. I was once a Jedi Knight, the same as your father."
...then it gets reduced to an off-screen conflict apart from the beginning and the end.
It's not even so much that the plot that sucks, it's how it's delivered. Phantom Menace is just the worst offender, but the others share a lot of the same faults - uninteresting characters (unbelievable achievement considering source material), scattered storytelling etc.
I wonder if Lucas would consent to a partial franchise reset, sort of like the recent Start Trek [sic]... except in a way that would make sense. No time traveling plox.