The Star Wars prequels were extremely poorly executed films, mostly because George Lucas never figured out how to write or direct characters There are some really interesting ideas buried in those movies if you go looking, though, which makes it even more frustrating
I think Lucas' biggest problem is actually creating medium- and long- term inertia in the plot. He does well with the form "immediate problem -> immediate solution," like the trash compactor scene. He is thus uniquely unqualified to direct an epic.
