This books is bad news, especially since it should have been such good news. Science fiction is in need of a good historical survey, but this isn't it. The writing is choppy and labored. The author endlessly uses phrases close to "this x reflects science fiction's central dialectic," but in neither the preface nor the postscript does he do an adequate job of explaining this dialectic. At times, the factors in contradiction within the dialectic seem to be as simple as the tension between technology and mysticism. At other times, Roberts has a more complex theory involving the interplay between Catholicism and Protestantism, which, believe me, don't ask. The narrative aspect of the history is awkward and lacks flow. The only primary sources used in the text is the science fiction itself; the author has apparently visited no archives. The bulk of the book is taken up by plot summaries. This is a synthetic history, and barely professional.
At several points, the author fails to cite the sources that guide his thinking. For instance, from 297-299, Roberts discusses how Thomas Pynchon's _Gravity's Rainbow_ lost out on the Nebula Award to Arthur C. Clarke's _Rendezvous with Rama_, but he never cites Jonathan Lethem's essay "The Squandered Promise of Science Fiction," which appeared in the _Voice Literary Supplement_ in 1998, nor does he cite Lethem's later exchange with Ray Davis, which appeared in the _New York Review of Science Fiction_. Yet, these pieces are obviously the origin of the Pynchon-Clarke comparison. Robert's work isn't plagiarism, but it comes damn close at times. It certainly isn't careful scholarship.
Finally, anyone who is well-read in the secondary literature on science fiction, including Darko Suvin, James Blish's work as William Atheling, and Thomas M. Disch's reminiscent _The Dreams Our Stuff is Made Of_ , will find that Roberts has virtually no new insights into the genre.
I will probably use this book as an occasional reference work because it is comprehensive. This comprehensivity, however, and its too long time span (400 AD-present? why?) makes the work thin. It's a lemon, folks.