I agree the dialogue needed work but Ewan McGregor did fine with it. Anikin and Padme didn't.
Well, McGregor is a better actor. But he also had much better material to work with. For one, he didn't have any inane love scenes that were just dead. The guy who portrayed the emperor did a great job, too (with the exception of that maniacal laugh), but here, too, he was given something meaty to work with.