A Science Fiction masterpiece. 
 I don't say it lightly, and I write as a former skeptic, disillusioned by a certain mini-series adaptation. The writing is precise and skillful. The peculiarity of there being only three book divisions and no individual chapters was a bit to adjust to at first, but the viewpoint transitions were clear and it made for a steady pacing that never slipped in momentum. The author even seemed to convey his female characters with a depth of understanding and respect that took me by surprise. The complete and comprehensive extent of Herbert's world-building was nothing short of spectacular. 
 I find I'm a bit appalled by the accusations I'd seen by those who seem to believe the author was attempting to convey some preference for chauvinism or homophobia. Ridiculous. True, the book pays no homage to the PC, but one could hardly expect that from a book published in 1965. 
 As to the religious aspects, it is heavy with a sort of warped fusion between Catholicism and Islam (Which is explained at some length in the Appendix 2). But it never really touches the heart of either belief system. I didn't see it as a philosophical attack on any particular religion, nor could I see it as some compelling enticement toward atheism. As ever, people seem to see in fantastical literature whatever they wish to see and justify...or wish to condemn. 
 As for me, I enjoyed it as a grand and artful treasure of a story.