I really loved this book. Usually, I don't like sequels of great books because the sequel usually stain the reputation of the first book (read: "World Without an End"), but this is a case of a good prequel.
For one thing, I finally could see Duke Leto being the incredible man that everyone talked about in Dune. I felt like we couldn't really get a good feel for him in Dune; he was a good ruler according to many, but we don't see facts of that. In this book, however, we see that he really is a dedicated ruler and a good person in general.
I really felt affinity for some of the characters, like Leto, Abulurd, Emmi, Rhombur. This book does a good job in creating the foundation for characters which appeared in the original Dune, and I could understand characters which we barely saw, like Duncan Idaho (which I felt didn't have enough strength in the original). I found his journey through the several islands fascinating.
All in all, I felt this was a good prequel, and a good book, even for those who haven't read the original. It explains a great deal about old characters and even introduces new characters. It was pretty satisfying, and it makes me want to read the Dune books. :D