This is a very general statement but I think film is just like music in that often times (actually most times) you can't really explain why you don't like a certain movie or album. Both film and music work at an emotional level and if something fails to grab you and be compelling it's often difficult to nail down what the reasons are.
Having said that, I still enjoy the SW prequels but I take them for what they are. They are meant to be straight up entertainment with stories and characters that are easy to understand. They are NOT meant to be in the same league as Blade Runner, Gattaca, Dune or other sci-fi movies with complex, adult themes.
I speak Spanish to God, Italian to women, French to men, and German to my horse. - Charles V