I don't know. The sequels decreased incrementally in quality, but by reading through to the end of God Emperor, at least I got the feeling of a story brought to completion.
I agree that the fifth and sixth books in the series were unnecessary. I found them quite tedious. I don't know whether I want to read the series co-written by Herbert's son.
Lord God Emperor could have benefited greatly by some editing. Like getting rid of around 100 pages by reducing the interminable speeches.
A lot of authors get like this when they get older. Heinlein’s and Asimov’s later stories were also long drudges of exposition and virtually unreadable. Unless of course one is a fanatic fan.