The first half is amazing. Boggled my mind. Then it started slowing down, and by the end I was just happy it was over with. A good thoughtful read, but why Herbert spent so much time dwelling on the Hayt/Idaho (is he, isn't he, what, when, why, how, blah blah blah) I'll never know.
It's a great sequel as it were, at least it doesn't let itself dictate by the success and structure of the first book, but on the other hand it almost felt like an expanded short story at times.
I'm going to be generous and give it four stars simply because the beginning was as great as it was.