Lucas is a great idea man but he's terrible at dialog.
I've heard stories of Harrison Ford going to Lucas with a script and saying 'Nobody would ever say this crap', then ad-libbing something better.
Plus Lucas' sense of humor has significantly devolved between the seventies and now, now he's focused on adorable children, cute fuzzy things and wacky slapstick.
Lucas can come up with good ideas for movies but somebody else should hold the pen. Otherwise, meeza Jar Jar and Jewish stereotype aliens.