Sandworms of Dune
By Brian Herbert
and Kevin J. Anderson
So if they had all these notes to finish the series why not finish it, why write all these other books? Well, simply they wanted practice. But a deeper reason has to do with the story. There are some vital elements that need to be understood before you read the last two books. That was their thinking, and now that I have read the last two (and all the books written before them), I agree with them.
The two books are very good. Even better than the last three. They bring the story to a great close that I think could really be related to current life, in many different ways. I did not expect the ending, and it was far better than what I could have came up with. I think these two men have done a fantastic job in keeping the Dune Universe true to franks dream, but instead of trying to emulate him, they made it their own, and they have done a wonderful job at it.
As to the order to read the series I recommend this. (I am only going to include books up to the point I have read. There are three more, but at a later time I will tell you where they should be read in the set.)
That is just my opinion, feel free to read them anyway you want. I am reading them in the order they were written. And because of life, the lengths of the books, and my poor memory, I felt like by the time I got to Hunters and Sanworms, I had forgotten important things from Heretics and Chapterhouse.
An alternative place to start would be Dune The Butlerian Jihad. And continue to read them in chronological order. When I catch up to the authors (that's correct, they are still writing books) I will read them in the chronological order.
I think the order I have given you is the best of both worlds. Because if you start the series at Dune and do not really care for it, its a self sufficient story, and needs no other books after it, making it a good place to start. And if you do like it, you can explore the universe in an order that should help you retain the information needed most to understand the end.