The fifth novel in the Dune series is a revival of the action and political machinations familiar to readers of the earlier novels.

Recovering from the doldrums of the previous novel, Frank Herbert is back in form with Heretics of Dune.  With nearly all of the familiar characters now dead his challenge is to make the new ones seem as innovative and interesting as when readers were first introduced into the whole mythology of the series.
For the most part Herbert succeed by focusing as much on the personal development of his characters as he does with attention to the laired political and economic maneuvers of the various power groups such as the Bene Gesserit and the Tleilaxu.  By admitting the readers into the minds of characters like Miles Teg, Odrade, Waff, and Sheeana—all complex and vastly different personalities—everyone gains appreciation for the interior lives and motivations of these characters.  This element was sorely missing in God Emperor of Dune. 

In with the New

In addition to learning more about the inner workings of established orders—such as the Bene Gesserit—readers are introduced to new forces such as the Lost Ones and Honored Matres.  While this infusion of new blood allows for interesting alliances and shakes up the old orders, the newer groups do not seem as fleshed out.  Much time is given to the inner workings of Tleilaxu society and their secretive religion, but when it comes to the Honored Matres, they remain violent and their motives inexplicable.
Such a lack of information is unfortunate given how well new characters are explored.  What makes the situation even more frustrating is that readers come to care about characters like Sheeana but never really understand the entities that threaten her.  At least in previous novels foes like the Baron Harkonnen and Alia had personalities and flaws that made them believable.  The only antagonist to get any similar treatment is Waff who is really only pitiable because his religious convictions are taken advantage of.

The Ghola Returns

The ubiquitous Duncan Idaho returns once more as the hinge for both Bene Gesserit and Tleilaxu plots.  His position is interesting, though, as he comes into his own and starts to questions his free will and makes choices for himself.  As such he a mirror of Sheeana who after discovering her talent with sandworms, begins to make her own decisions and discover her own path.  These free-spirited characters are interesting foils for others like Miles Teg who views everything through the lens of honor and loyalty, virtues instilled in him by his Bene Gesserit mother.

Changing of the Guard

The plot in Heretics of Dune takes a few chapters to get going but steadily increases the tension until the climaxes of Duncan and Sheeana’s interaction, dealing with the sandworms, and the fate of Dune itself.  The characters grow organically, largely through reflection and interpreting events through their particular worldviews. 
Herbert’s style still has its trademarks—italicized thoughts, passages of exposition, and epigram lead-ins to chapters.  Though these can wear thin, especially when he gives detailed exposition for relatively unimportant development but leaves elements such as the Scattering virtually uncommented on, they do not derail the trajectory of the novel.  Longtime fans might be saddened by events in the end, but the future of Dune appears secure enough to enter into its new era.