It is Herbert's worst written Dune novel thus far. He's developing too many plot threads all at once, which causes things to progress merely inches across hundreds of pages. He also created the unfortunate burden for himself of having to fill these hundreds of pages with the words and psychology of galaxy brain thinkers, moving from the Benne Tleilaxu, to various Benne Gesserit witches, and brilliant ghola and Arrakeen mystics, and the new sex witches, the Honored Matres, which results in the book having this corny pretentious tone. More than ever, the knowing factions of this universe talk to each other in the same fashion you would expect chance meetings between high IQ reddit posters or Joe Rogan fans to play out like. I don't think I would write this book any better than Herbert, but I might have done things different if my goal as an author was this ambitous; especially if I had all the experience with writing novels, and sequels to novels, as Herbert had. So for producing such an unwieldy and dull novel, I think you really have be honest and say this is a big failure.
Don't misconstrue this as a recommendation to avoiding reading Dune sequels. All the previous Dune books are well worth reading. It's actually sort of a miracle that this series stopped being good only at its fifth entry.