Possibly the best science fiction novel ever. The sequels and prequels co-authored by his son are dreck, however.
I agree that Dune is a masterpiece, but the first chapters where Herbert sets the scene on Arrakis and introduces some of the players are tough to get through. Building a fictional world, peopled by all sorts of semi-humans, non-humans, and protohumans takes a little time.
Well worth it though when you finally begin to comprehend a little bit of what's going on.