I've said this before but Dune is one of my favorite books of all time and I love the film as well. To me they have an almost symbiotic relationship. I always recommend to people that they read the book, then watch the film, then read the book again.
The film doesn't work without understanding the book, but somehow the visuals and atmosphere of the film improve the book on subsequent readings. It is an incredible feat of vision.
It is a rare thing indeed for a film to improve on your minds eye. I think the original LOTR film is the only other example I can think of, although in that case I remember feeling very clearly that this was how I imagined it.