I've long held the first Dune novel high on my list of good books, but only recently I've gone through the following 6 (as audiobooks), and I highly recommend them. The scale of ideas and events absolutely dwarfs the first novel.
I used to have a copy but sold it at some point. Apparently it's hard to find now, given the very high price.
Update: The entire book is in the Internet Archive! https://archive.org/details/the-maker-of-dune-insights-of-a-...
https://www.oreilly.com/tim/herbert/
Edit: I see Tim O'Reilly was the editor of the "Maker of Dune" book mentioned here also.
Then stuff happens near the end and it's good for a bit then it's over.
I now emphasize with leto. I was a alumni advisor for a student group (fraternity). I had to start checking in every quarter with them because of this. It was amazing because every 3 years everyone would flip over and if I didn't ask they'd literally come up with the most obvious idea. They'd tell me and I'd be like "this (simple failure/hilarious failure/prison term) is why you shouldn't do that"... to which they'd go oh makes sense and go onto the next idea. Often this was cause they wondered why things were more complicated than you'd think.
Wait now that I think of it that's similar to work now that I've been there for a while. Or with Jr Engineers. I guess I should stop thinking of it so negatively and look at it like teachers, another chance to watch someone learn. https://xkcd.com/1053/
The structure is unusual in that it's essentially the journals of an omnipotent tyrant with a chokehold on the universe musing about the nature of man and the universe for 400 pages while being very light on plot; a big change from the other books in the series. I think it's a fertile concept to spend an entire book on and I find Frank's observations stimulating. He's crafted such a unique character; someone who can not only see into the future, but can access their entire genetic heritage and the memories of their ancestors. That makes for some very unique observations and I am here for it.
It's my (admittedly slim) hope that we'll someday get the Worm on screen. I have no idea what that movie would be like or if it would be any good, but it would certainly be ambitious.