Aw, you gave up at four? But in five and six the Bene Gesserit actually become the main characters! Annoying Leto II is out of the way and Herbert seems to...like, suddenly decide that the Bene Gesserit are worthy of much of the screentime and coolness. And they also begin to lose that "secretly sort of evil and meddling" veneer they have in the early few Dune books.