I used to warn young readers, "Frank Herbert got flicked on the head one day by God; he saw the glowing words, wrote them down, and produced one of the 1/2 dozen greatest SF books of all time. Unfortunately, he tried to write the next 4 or 5 on his own." Actually I believe I read that Herbert did get an inspiration while working on another book that was going slowly, and knocked out Dune's 1st editor's draft in about 3 months.
LOL!
Wife, the librarian, who consumes critically reviewed (and quite a bit of 'other') SF like the Doctor ate jelly babies, warned me off the Dune follow ons, then later said that the last one was apparently worth it. I did get about 1/2 way through the 2nd one (Children?) before the stamina gave out. I skimmed a couple of the others.
i'd agree. the second book is just... well, it's about as appealing as jarjar binx. but it's also the shortest of the six originals.
i thought the third was really good. the forth was exceedingly strange and meandered to the end of the book. but the fifth and sixth were utterly fascinating! though the end of the sixth book sort of threw me for a loop... i'm still not sure i 'get it', let alone if there's something there i should be getting.