I feel the prequels didn't need a lot of radical changes to be a lot better. I recently rewatched Phantom Menace (which I'd always liked since I first saw it in '05) and I still think it's decent. Call me crazy if you want but that's my opinion.

However, I feel the script was merely a very good draft. It needed someone to say "this is pretty good George, but it still needs some tweaking." I think the bad acting was mostly a result of bad writing and ineffective directing. It's almost like the actors weren't allowed to intereact and have any sense of spontaneity.

I know a lot of people hate the midiclorians but from a pacing standpoint, they were also done poorly. The scene where Qui Gon explains to Anakin about them is a total info dump, the movie stops cold for exposition. Considering that the force, the Jedi abilities or lightsabers and even the Jedi mind trick were never explained in this movie, did we really need to have a wikepedia entry on midiclorians in the middle of the movie?

So to sum up, I think if the movies had been done better, people would have been more forgiving about the plots.