Number four down on my "Reread/read Frank Herbert's Dune series" project. And it's a mark of my particular psychological quirk that makes me go on, because it's no fun at all for me.
One excuse: it's been sitting on various bookshelves of mine since I got it (from Science Fiction Book Club) back in 1981 or so. I bought it, I really should read it.
So far this has outweighed the obvious counterarguments: (1) That is a literal sunk cost fallacy. Also literally: (2) life's too short.
It's set on Arrakis, about 3500 years after the previous book. The planet has been largely terraformed with open water and lush vegetation. Sandworms are pretty much extinct. Except for Leto II; his hideous transformation (begun in the previous book) has made him into a human/sandworm/sandtrout mixture. Not very big as sandworms go: a mere seven meters long, two meters in diameter, massing about six tons. With a "Atreides face", hands and arms "still quite recognizable as human", but legs and feet atrophied into flippers. And he gets around the planet in his "Royal Cart". He's set himself up not just as Emperor of the known universe, but also as a god. (Really. The title is not kidding.)
Like his father, Paul, Leto II has the gift/burden of precognition, combined with the collective consciousness of his ancestors bubbling around his nervous system. His plan is to set mankind on the "Golden Path", avoiding its otherwise inevitable self-destruction. This involves a certain amount of ruthlessness and spouting of oracular bullshit. And (as in the previous books) a string of Duncan Idaho "gholas", manufactured from the original genetic material by the Tleilaxu. (Leto II keeps killing off the Duncans when they get too obstreperous.)
As in the series' previous entries, there are long stretches of text where characters yak pretentiously/portentously at each other. ("You dread the imperialism of consciousness, and you are right to fear it," Leto II says to his majordomo at one point. Really? And there's page after page of stuff like that.)
But occasionally things actually happen, including some apocalyptic ultraviolence at the very end. It's a page-turner, but not in the "what happens next?" sense; more like the "gotta trudge through this" sense.