Personally, I am a proper Dune fanatic. Dune is the War and Peace of speculative fiction, and, yes, I say that believing War and Peace is the greatest novel yet written. Dune, too, encompasses everything:

• War
• Peace
• Guerrilla tactics
• Religion
• Fanaticism
• Time
• Space (tesseracts)
• Love
• Death
• Psychology
• Compromise
• Ecology
• Legend
• &c…

The plot is intricate and deeply thought out, several of the characters can break a reader’s heart, and the world-creation is quite simply complete.

I first encountered the Dune world at age 13, through the David Lynch movie adaptation.  I read the novel immediately afterwards, and since then have owned somewhere on the order of a dozen copies, most of which I have given away (indeed, the purpose of having extra copies on hand).  I generally try to start reading the book slowly with lots of processing time; this works with many books I love, but in the case of Dune I am inevitably absorbed, and I career through the last 150 pages in a short evening.  I am left feeling somewhat heartsick each time, for Dune ends but does not resolve: the story is wide-ranging and messy, and even the “right” solution to the crises involve lots of death and–worse–soul-destruction and the breaking of barriers that protect people, like self-preservation.  None of which will be forgotten or forgiven, the ending makes clear.  I love the story for its truth to life that way. 

I have seen a friend become a creature.

In my family, I should note, “proper Dune fanatic” means that we attempt to forget the existence of all series books subsequent to Dune itself.  Or at least to spare ourselves any interaction with them.  Dune ends openly, and so theoretically open to sequel, but Herbert was quite evidently utterly unable to keep up the intensity of engagement that any true succeeding volume would have required.  I don’t necessarily hold this against the author; I have been told that many of the subsequent books were written to make money for Mrs. Herbert’s medical bills, and I tend to imagine that Dune as a universe is something powerful enough that it existed (somehow) prior to the books, while Herbert merely (somehow) saw it and tapped into it.  Which is a great accomplishment in and of itself, and should be enough.