Anybody interested in the possibilities of a great Dune movie NEEDS to watch Jodorowsky's Dune. This is an absolutely fascinating documentary about a pre-Star Wars attempt to get an epic version of Dune off the ground, that had it come to fruition, would have changed the course of cinematic history.
The film looks as though it would have been incredible, and is packed with amazing ideas about how they would have brought it to life, but even more interesting is to see the depth of impact an unmade film has had upon Sci-Fi since. It's designs and ideas are strewn throughout subsequent films like Star Wars, Alien & Blade Runner.
To be frank and IMHO, Jodorowsky's Dune was most likely caca of the highest order, and would have flopped at the box office and been blasted by fans of the novels. At least Lynch got the tone right.