CO hit a major point--this was the only time when Lucas took a chance, when he stepped back and let someone else play in his world. For sure, ESB is the only SW film that is different, that FEELS different, that has a distincly personal artistic stamp on it--that is the stamp of Irvin Kershner.
If you read all of Lucas' interviews from 77 and 78 he basically wanted to have a james bond series, where every year a new director would have a go at the continuing stories in the star wars universe. ESB, more or less, was the only time this happened. But because the production was so immensly troubled, nearly a complete failure, and the film so unlike the way Lucas would have directed it, Lucas basically canned this plan and got himself a puppet for ROTJ, which was Richard Marquand. Okay, puppet is too harsh, but he wanted someone who wouldnt oppose his ideas and style the way Kirshner did, and as CO put it, "play it safe".
If you read the interviews, everything is about this massive serial saga that is at least 12 films long--then ESB goes into production and is met with problems every step of the way, nearly destroying Lucas but ultimately being a success. Suddenly the tune changes--ROTJ will end the saga and then "Somewhere down the line, maybe, possibly, one day" there will be a sequel trilogy. ESB was so heartbreaking for Lucas to make that he basically quit. And even then his personal life was in such shambles from making the films that his marriage didnt even last to ROTJ (he may have actually been divorced the month it opened).
Anyway, what i was starting with was that Kershner is definitly NOT to blame, and everything good about the film, everything that sets it apart from the rest, comes from him. The problems on the set all go back to Kurtz, if any one individual is to blame.