I'm not sure if I've ever agreed more with a post written by someone who wasn't me. George Lucas is/was an "idea man". He's good at letting his imagination run wild and coming up with all kinds of stories, characters, environments, etc., but he doesn't seem to actually know how to do anything with that information. Back in the days before Star Wars Lucas was an impressionable college student who had friends like Francis Ford Coppola giving him notes on his scripts. So he makes a few movies, somehow manages to create a couple that strike a chord with audiences and make a lot of money, and he's suddenly expected to duplicate what essentially amounted to dumb luck. He tried, but even he quickly realized he's far better at "delegating" than "doing". (It also gave him someone to place blame on when things didn't go exactly as he wanted, but that's another discussion for another time.) So he becomes the king of his own hill.
I'm convinced the only reason he made the "Prequel Trilogy" Star Wars movies was to stop the fans from asking him, "When are you going to make another Star Wars movie?" He never intended Star Wars to become his entire career, but that's how things worked out for him because his fans didn't seem to care about anything else he did.
Well, except for his participation in the Indiana Jones franchise. Even then, as I understand it, he's the "story guy". He, Steven Spielberg, and Harrison Ford, come up with story ideas, Lucas hires someone to write the script, Spielberg directs, Ford stars. It must be nice to get paid so much for doing so little.
My favourite comment on George Lucas is the persistent rumour that the reason Peter Jackson - after all those comments about having "spent enough time in Middle Earth" bought the rights to The Hobbit purely because he'd heard Lucas had expressed an interest in doing it, and he didn't want it ruined!