Book five y'all: Heretics of Dune.
Frank Herbert certainly takes the long view when it comes to the epic saga, boy. So, some time has past in the narrative since book four, but the story of the Dune universe pushes forward. This book, in a lot of ways, seems to be laying the groundwork for the finale, which I presume occurs in the last book in the series. Bridge books are fine, as long as they are entertaining and continue to move the story forward, and that's the case here. [I just looked back at what I wrote about the second book in the first trilogy: Dune Messiah. I called that one a bridge book too.]
So check out the cover; sandworms are obviously still a part of the story, that much is clear. Paul Atreides, or Muad'Dib, through his progeny are also, is still very much a part of the narrative, but Herbert has deconstructed the original story and re-built a new storyline from its parts. What's that mean for us readerfolk? A sequel-ilogy that reads pretty well on its own, has some of the familiar elements, but isn't the same old story warmed over to cash in on the readership. In other words: so far, I think the second trilogy is pretty good.
This volume also revisits some of the more peripheral elements from the earlier stories, and brings them more center stage. The Bene Gesserit and the Tleilaxians for example, get a little more in depth review in this book, the Tleilaxians maybe more so than the BG, only because the BG were pretty well delved into in earlier stories. I'm dancing around here because I don't like spoilers so thats probably as far as I'm going to go.
I burned through the last part of this book, and I'm looking forward to the last book. Not sure what's next yet. The Cicero books aren't all out yet here in the US so that's on hold for a while. I've got The Prince by Machiavelli on deck, or I might just jump into Asimov's Foundation series after reading Orson Scott Card's short story a little while ago.