I love Raiders. Awesome flick.
I think Kasdan's story and Kirshner's direction are what made Empire so great. It was a very dark story and the direction fit the dark tones. Plus, the art department did an amazing job. It seemed like things were looking up and they were even on the bright, beautiful cloud city. Then Vader showed up and the whole tone changed back to dark, and the sets changed with the tone. Very well done. Plus, the story is just fantastic.