Personal trivia: I apparently got this when I was still a member of the Science Fiction Book Club. ("Book Club Edition" on the dust cover flap.) It's still holding together, though. I don't remember reading it back then, I think I just bounced off it.
The front cover of this edition says, breathlessly: "The Climax of the Dune Trilogy". Promises, promises. Frank Herbert followed up this 1976 novel with three more, in 1981, 1984, and 1987. For some reason I bought them, and they've been sitting on my shelves uncracked for years. Someday, I hope. They're in my TBR system, anyway.
Frank Herbert's son Brian has collaborated with Kevin J. Anderson on approximately 786 sequels and prequels since then. Not purchased, not gonna read 'em. Life is literally too short.
Anyway, this book: Paul "Muad'Dib" Atreides has gone AWOL, wandered off blindly into the Arrakis desert, presumed dead. But his twin kids, Leto II and Ghanima, are around, and they're both wise beyond their (nine) years. Unfortunately, they are the target of a convoluted assassination plot, involving genetically manipulated killer tigers.
Paul's sister, Alia, has sadly succumbed to the Dark Side, allowing a past (dead) villain to shape her nefarious activities. And there are big changes on Arrakis, thanks to large-scale ecological engineering: water is plentiful in some areas, the area controlled by sandworms is shrinking, and this (of course) has impact on the production of Melange, the vital spice allowing interstellar travel. Also appearing: Paul's mom, Lady Jessica; the Duncan Idaho ghola; Gurney Halleck; Stilgar. And some new folks, including "The Preacher". (Who just happens to be a blind guy from the desert. Hm.) And sandworms, always nice to see them again.
So things happen. A number of people die along the way. But there's a constant drumbeat of pseudo-profound balderdash and mystical bullshit permeating the book. In dialog, inner monologue, or just exposition. You have to wade through it in case something relevant to plot or character is revealed, but that almost never happens. Example: At one point The Preacher yells at Alia in a "rolling stentorian shout": "Abandon certainty! That's life's deepest command. That's what life's all about. We're a probe into the unknown, into the uncertain."
For the record, Alia does not respond: "So what? Unhand me. You're a crazy bad brother." That would have been good.