I’ve seen three versions of this movie. The theatrical and the longest one both sucked for anyone not a Herbert fan. I thought the longest was the director’s cut but he never did one. Perhaps it was the TV movie cut. But I don’t know what the “good” one was called.
I blame this on the muddled mess that was the release edit and how misleadingly the film was promoted by the studio. I was a huge fan of pop sci-fi like Star Wars, Alien and Blade Runner and the advertising set a very different audience expectation than what the film delivered. Unfortunately, that experience kind of tainted Lynch's Dune for me.
I didn't really begin to appreciate Lynch as a great filmmaker until Blue Velvet and Twin Peaks, both of which I loved. Someone linked a 'highly-regarded' three hour fan edit of Lynch's Dune which I've bookmarked to check out.