I believe Lucas is (or at least was) a good director, but he just doesn't have the ability to stick to a larger viewpoint. Beyond the time length of a movie and other simple elements, he seems to struggle for a proper perspective with things such as story. Everything with him is tunnel-vision and that's what leads to his latest movies being terrible. (I should say though, that I've never seen any of his non-Star Wars movies.)

In terms of acting, I'm guessing George is just a cold, withdrawn man who doesn't care about well-performed drama. He also needs others to help him make a story that reflects the softer or more humorous side of life. Alone, he makes something dry and dull.

How old was his kid when he made Episode One? Maybe that's why it's filled with juvenile humor. Perhaps that was what was influencing George at the time.