I am a person with (as usual) an odd take on this question. I think Dune is one of the best badly written books going. The ideas are fantastic, but the style is horrible -- often turgid prose, many of the author's major points glossed over, wildly shifting PoV, etc.
Herbert, at his death, was also one of the most bitter writers in the world. According to an interview with him just before the Lynch/DeLaurentis film (and it is important to remember these two wildly divergent people were involved in the project), the film was horrible and all films made of it would be horrible. To paraphrase him, Dune was about one thing and one thing only: fanaticism, in any form, is wrong. Thus, according to Herbert, Paul Atredies begins the book as a Good person (working against the fanaticism of the empire and the Harkonnens), but ends the book as a Bad person (leading his Fremen on a new jihad across the universe). Herbert was upset that his fans didn't see that Paul had turned Evil, so he wrote the very short sequel to underline the point. The fans ate it up and still loved Paul. Herbert was appalled and felt that, for his bank account, he might as well keep writing, but he no longer loved the books and he was upset that no one read any of his other books. In his own words, "My fans don't give a damn about quality. I could write Garbage Scow of Dune and it would be a New York Time's best seller."
**ouch**
So I have a very odd feeling about Dune. I have read it twice. I think many of the ideas are good, but, like I said, I don't think the book is very well written. That and I feel sorry for the bitter man who wanted to write one thing and ended up with an entirely different fanbase.
