I'm a big Silverberg fan, but I find it kind of perplexing that this is his only major award winning novel (Nebula, 1971). I thought "Tower of Glass" and "The Stochastic Man" were much better. But then again, if you read the recent edition of this book, with Silverberg's updated preface, you gain a lot of insight into the work itself, particularly as it pertains to the changes in Silverberg's own life during the novel's crafting. It's this personal aspect, which I think detracts from the universal appeal present in some of his other works, that makes me withhold a better rating.