Lucas' contribution to the Empire script can't be underestimated. The bold structure, the ending, the radical departure from Star Wars, that's all Lucas, and Kasdan is the first to say so. George SUCKED at the Han and Leia dialogue however, (and he admitted it, which was very cool) and that is where Kasdan and Kershner came to the rescue. It also helped that Kershner is apparently the only human being on earth who can coax subtlety out of Carrie Fisher.

edit-oops, I meant overstimated, my duh.