I think one of the reasons it took me a while to see just how bad the RotS film actually is was that I'd read the novel first. The book, while essentially the same story overall, is very well written and in particular the turn to the dark side felt like it made a lot more sense. Since I had those notions in my head already while watching the movie, the differences and nonsense didn't become apparent to me until later on. I always knew something was off about it, but for a long time it was only a vague feeling I couldn't articulate and tried to ignore.

I haven't actually read the book for quite a while, but I probably will again at some point. It's still not even close to the way I actually think of the Empire being formed and so forth, but it's a more palatable version than the movie at any rate.