This is one of my favourite of the Dune series. The focus of the book stops being the Atreides family and pivots to the Bene Gesserit. We also lose the theme of being trapped by fate that dominate the previous books. Instead the Bene Gesserit have to deal with a bastardised version of themselves from the scattering. The book also explores the interesting notion that by copying something so precisely there may eventually be no difference.