Long, layered plots, and who knows what humans 8000 years in the future will be like? I must admit that I've never read "Dune," so I'm taking it on faith that Smithee is being reasonably true to Frank Herbert's tale. The film takes the three predominant religions of our times, Judaism, Christianity, and Islam, and combines them in a way that needs some 8200 years into the future (if, indeed, the year 10,191 is based on the Christian calendar) to pull it off. Since we don't know how humans eight millenia hence might behave, the producer was free to have them do whatever he wished. They certainly have all the weaknesses and strengths of contemporary humans, so, apparently, nothing has changed much -- except that technology and some mind-expanding material, Melange, enable humans to "travel without moving."
This film has numerous plots and sub-plots, so it takes some time to develop them in a way that makes sense. "Tinker, Tailor, Soldier, Spy" moved along in a similarly slow and careful fashion. As for the acting, some of it seemed a bit melodramatic, but again, we have to accept that humans some 8200 years hence can be whatever the director wants them to be.
While the 137 minute US version is just barely enough to make some sense of the story, the full-length version, which provides an explanation for some of the seemingly disjointed action, is more than most people will sit through voluntarily. On the other hand, if I hadn't read Arthur Clarke's "2001: A Space Odyssey," before I saw Kubrick's movie I wouldn't have understood some of the strictly visual scenes that occur at the end of the film.
I liked the film for the way in which it mixes religion and human nature.