Dune is a fantasic book. It's clever, interesting, and entertaining. The audiobook edition I got from the library was extremely well-produced, and I thoroughly enjoyed listening to it.
Dune Messiah, on the other hand, was not. Instead of calling it a novel, I'll call it a treatise on god-kings. It's a philosophical work much more than it is a story. It's completely uninteresting. There is no story line to speak of, and the characters are not compelling.
Children of Dune is much better than Dune Messiah, to be sure, but it does not live up to the standard set by the first book. Sadly, the tendency still persists to wallow in pseudo-psychological examination of the character's status as a god and what it all means to the universe.
In short, I would recommend Dune (and should have read it earlier... I was very, very late to this party), but I would not recommend the two sequels.