He had substantial creative support for writing ANH, and the superb acting in that film is largely because of Alec Guiness' seasoned talent, and the other actors improvising for themselves. It's nothing to do with Lucas being a good director. He was bad. Really bad. On all accounts during production, the guy was sorely lacking in the social skills department. "Faster and more intense, CO."
ESB was neither written nor directed by Lucas. Kasdan wrote the script, and Kershner directed. Lucas was on the other side of the globe during most of the production.
And American Graffiti I don't see as being anything to write home about, and THX-1138 I've only watched clips of (didn't interest me). That's preferance, though. I'm trying to bring around the idea that the more control Lucas has over a Star Wars film, the more it's panned by critics and fans.
I respect your choices on what you like and don't like by Lucas, but I just don't think he was a hack in the 70's. As I said, I think he was well past his prime by the time he filmed TPM, and he lost that edge that he had before he was a billionaire.
I just think there are 2 Lucas's, pre-SW1977 and post-SW1977, and the pre-1977 could have had a nice career as a director if he wasn't swallowed up by SW-mania. Coppola even said, "The success of Star Wars robbed Hollywood of a great director."
As for comparing sequels to their originals, I could say the same thing about Lethal Weapon IV compared to Lethal Weapon, is that the same director? Richard Donnor directed Superman I, Lethal Weapon, and many great films, and then I see Lethal Weapon IV, and that was an utter piece of shit, that sorta ruined the series to me, but again, I think Donnor was well past his prime by 1998, and lost that edge that happens to most directors. Only guys like Scorcese and Spielberg have been consistent in their movies their whole career.