I think the Harrison Ford interview in that clip from A&E's Empire of Dreams is very telling. Lucas basically wanted the actors to just do what he wrote. It's on paper, do it. Well, his scripts have been weaker this time around. While he is a great visionaire, he can't bring performances out of an actor like Spielberg or Scorcesse can.
I still think that if TPM hadn't been so miguided, we would not have been on him so hard for AOTC. It's very watchable, almost good if you ignore some goofy dialogue.
Basically, don't blame the actors. They aren't all Tom Cruise, they can't invent their dialogue and the script to their liking.
But I agree, let's face it....ain't none of them Sir Alec Guiness.