Sometimes I wonder if Han couldn't have been used better for what he was. He was supposed to be the anti-hero of the first movie, and he did a pretty good job of that, but, of course, he redeemed himself at the end of the movie by saving Luke. Empire still had some of that. His original motivation was to get back to that, but it never really worked out. And, of course, in Return, they'd pretty much given up on his character moving at all. So, really, both the sequels wasted that character (as in, there's very little ambiguity in Empire and absolutely no development in Return) as it was originally conceived.

(But I still like what they did do with him in Empire, don't get me wrong)