The biggest flaw with the sequels is that they end up not ending- in the same way the Dune Messiah was a setup for Children of Dune, it seems that Heretics and Chapterhouse were leading up to the seventh book that Herbert died before writing.
His son Brian and Kevin J Anderson did write the last installment based on detailed notes from Frank Herbert, so at least the story is complete.
While their writing is not as brilliant as Frank Herbert's, the books they wrote, mainly the prequels, have helped me understand just how big the original vision was and have helped me enjoy the sequels more. God Emperor is truly as masterpiece, but it took a couple of reads, and the sequels, for me to appreciate it more.
Correction: Brian and KJA had access to detailed notes from Frank Herbert, and used none of them in favor of KJA's "improvements" to the Dune mythos.
The same way KJA "improved" Star Wars.
His wife, incidentally the editor-in-chief of the publishing imprint that then owned the publishing rights to the Star Wars and Dune literary universes, is to blame for unleashing his word vomit on mankind.
There seems almost zero chance that the notes will be released. Brian has been increasingly adament about it, largely because a lot of people are vocal about suspecting they don't exist.
(I personally do believe that some notes were left, but I suspect they were not complete, and were utterly ignored by Brian & Kevin. Because they is no explanation which makes more sense. There's no way he would have tied up with series by referencing characters never-before introduced from before the previous books.)
I dunno, when you re-read Heretics and Chapter House after knowing how it ends, you can see some set-ups for the ultimate big-bad. And Sonia's vision in God emperor does also link up.
So, maybe? I lean towards thinking there were notes myself, as I can't see anyone making up that ending de-novo.
I can kinda see the argument, but the fact that the Butlerian Jihad was so rarely referenced in any detail makes me skeptical that the long-overthrown machines could arrive spontaneously and be the big-bad.
It seemed to me that the two figures in Duncans visions were going to become important, but they'd be rogue/evolved/advanced face-dancers rather than representatives of the machine intelligence.
I guess we'll never know for sure unless the notes are published.
Seriously, Sonia's vision in God-Emperor is of humans being hunted down by machines - this is what the Golden Path was to avoid. So, I'm inclined to err on the side of the notes existing and mentioning machines.
Siona's visions were about the danger of presience and the need for mankind to become free from those who would use fate/predestination as a means to control mankind. Avoiding the predestination paradox was literally the reason Leto created her.
Given the lengths that Frank Herbert went to avoid having computers in Dune, it would not make sense for his big bad to be a computer revealed in the last few pages of the series, especially when his big bad was always intended to be Destiny.
