I came to this book curious as to Campbell's renown as Britain's premier practitioner of the horror genre, previously having read only his short stories. Frankly I came away with no little bafflement as to the grounds for this reputation.
There are several worthy aspects to this novel: Campbell's imagery is genuinely disturbing, subtle and free from cliche; the attempts (perhaps neither, unfortunately, entirely successful) to address issues of religious fanaticism and nuclear weaponry - both still timely twenty years on; he also takes the trouble to paint his scene broadly, taking on a large cast of characters, most of whom are skillfully imagined. But this wide range is also one of the problems - there is simply too much content in the book, and furthermore, the quality of writing is somewhat uneven. I felt the novel was slightly too bloated, and its pace, although never exactly slow, overall a little too pedestrian.
And although Campbell generally avoids the more tedious staples of genre convention, some of the tropes are too wooden (one of the other reviews on this site nicely enumerates these creaking plot supports). Finally, although the prose is generally well wrought - transparent in its description and so on - it does stumble at places in the middle and towards the end of the book; although Campbell complains of being over-edited in his afterword, there was sufficient clumsiness in parts of the text to suggest that quite the opposite might be true.
All in all, the novel was perfectly readable, but not quite up to the standard of excellence I had hoped for given the author's good name.