I don't really know what I wanna get out of this post, but I recently finished my 16th book in the Dune universe, and I have a mixed feelings about the whole thing. Incase you aren't too familiar with the franchise, I think a brief explanation is needed.
Dune was written by Frank Herbert in the 60s. The original book is masterfully written and created fascinating characters and places. Herbert wrote an additional 5 books which followed the story laid out in the original - with gaps of thousands of years between a few of the books. Although the first is probably the best, all of the books are great. Unfortunately, the last book ended with a lot of unresolved answers (more so than the first one, which can be read by itself), but now I'm getting a bit ahead of myself...
Frank Herbert died shortly after the release of his 6th Dune book, and Brian Herbert (Frank's son) and Kevin J. Anderson decided to continue writing books set in the Dune universe. They started by writing a trilogy of books set a generation before the initial Dune. The trilogy was pretty horrible and should be avoided. They don't ruin the originals in any way but they just aren't very good. I was always disturbed by how violent and graphic the books were - obviously trying too hard (and failing) at making the reader feel what the original achieved so seamlessly: emotion and empathy and a real stake in the characters. The Harkonnen's didn't need to rape anyone in the original Dune for you to hate them (just like we didn't need to know about midi-chlorians to grok the force).
Another trilogy followed, this one set 10 000 years before the original Dune. Brian and Kevin clearly benefited from the experience of the first trilogy, as well as distancing themselves from the original Dune. It was a good story and well written. It also explained much of the history behind the organizations of the Dune universe (Spacing Guild, Mentats, Bene Gesserit, ...) without being lame.
Now, despite the fact that Dune under this new stewardship was a shadow of its former glory, I think most hardcore fans were still excited to get the conclusion to the original story. Brian and Kevin wrote two books to tie up the loose ends. Given how important these books were, Brian and Kevin clearly worked hard at making them feel like a natural and fitting continuation - and for the most part, I was happy with the books (they gave me the conclusion I sought).
Next came two books which focused on the events before and after the first Dune book. So far, this series has been pretty garbage - sharing a lot in common with the original trilogy. They feel so small and unimportant in the scale of Dune and they go out of their way trying to explain things better left unexplained.
But...my real problem with the last 4 books, something that continues to gnaw at me, is that I can hardly read a page without feeling like Brian and Kevin are trying to force me to read their first two trilogies. You see, they continuously make references to events described in their previous work...obviously and continuously. Its almost like you are reading a commercial for their other work. Initially I could forgive it because maybe Frank really meant the original story to come full circle. But the last two books, which really have nothing to do with the story, are filled with the same self-promotional crap.
Ultimately, the original Dune series (and the first book in particular) were written by one of the greats of science fiction. The newer books, not so much. Its a bit like LOTR to Harry Potter. Mind you, Brian and Kevin have clearly grown as storytellers over the years. If only they could stop trying to pimp their horrible Prelude of Dune and average Legends of Dune series. Also, it would be nice if they stopped trying to over-explain things that shouldn't be explained (like the Golden Path).
Long story short? Read the first book. If you like it, read the rest of the original books. Then find a summary of how the story ends.