Because science fiction takes science seriously and because science takes the laws of nature seriously, the s.f. writer cannot simply let his imagination run free when he creates characters, setting and plot; he must always appear to be following some rules—even if he has to make them up himself. No one knows this better than Frank Herbert, whose favorite theme, appropriately enough, is the nature of godhood and what happens to men who reach for it.

[In "God Emperor of Dune"], the fourth but not necessarily the last in his best-selling Dune series, Mr. Herbert reshuffles all the elements of the fictional universe that he created in previous volumes. I cannot imagine anyone making sense of the story without having read the first three books. At times, Mr. Herbert's energy flags; and, behind the understandable world-weariness of his 3,000-year-old hero, we sense the weariness of an author trapped by his own success. Yet against all odds, "God Emperor of Dune" compels belief. (p. 15)

The real fascination of the Dune books was Dune itself. So completely did Mr. Herbert work out the interactions of man and beast and geography and climate that the first novel, entitled simply "Dune," became the standard for a new subgenre of "ecological" science fiction. (p. 28)

Since Dune itself has lost some of its interest [after three books], Mr. Herbert draws on the vast galactic background that he has built up in previous books. The problem with most fiction set in the far, far future is that the author must invent just enough but not too much: If his imaginary world seems too familiar, we refuse to believe it is the future; if it is too different from our own, we cannot empathize with its inhabitants.

Frank Herbert gets it just right. By postulating a series of Luddite reactions to technology, he earns the right to limit his mechanical marvels to those that will advance his story…. Other authors have invented galactic empires with medieval power structures. In most cases, the motivation seems to have been laziness. Mr. Herbert makes it plausible; we not only believe in Leto's agon, we care about him and the self-deluded race he insists on saving.

By the end, however, I had the strong feeling that the resources of both Dune and its universe were exhausted. Frank Herbert hints that the manner of Leto's sacrifice will bring the desert back to Dune, which implies yet another book in the series. For the sake of the author, the Fremen and future readers, I hope this is not the case. Even Gods must learn not to repeat themselves. (p. 28)