My only real grip against Lucas is how he's messed with the original trilogy -- and basically it's just his changing of the original Star Wars and Empire. But I think he actually improved Jedi because that movie stunk even in '83.

And while the prequels aren't masterpieces, I enjoy them just fine. I expect Sith will become my 3rd favorite Star Wars film.
I also watched THX 1138 the other night for the first time and I really like that movie!
And if you look at Lucas' contributions to the world of film production/technology (sound, editing, special effects, etc.), he may actually be the most influential filmmaker in cinema history.