If you approach this book as mindless entertainment you probably won't be terribly disappointed. Of course, neither will you be wholly satisfied. The book has an interesting premise but one that is perhaps impossible to deliver on fully.
The main character, Kees van Loo-Macklin is the most brilliant, ruthless human the known galaxy has ever dealt with. It is, of course, very difficult for an author to realistically portray characters who are smarter than themselves. Foster tries to get around this by rarely having Loo-Macklin in the narrative. Instead, most of the story is told from the viewpoint of the one alien who devotes his entire life to trying to understand Loo-Macklin. This has the unfortunate effect of making the alien Nuel seem more human than Loo-Macklin. So not only does the author seem unable to realistically portray Loo-Macklin, he further disappoints by giving us an alien that doesn't feel very alien.
The removal of Loo-Macklin from the main narrative, while understandable both because of the difficulties of accurately portraying such a supposedly brilliant and ruthless person and in an attempt to keep him as mysterious to the reader as he is supposed to be to the rest of the universe, ends up being the biggest problem with the book. The reader is simply left with very little reason to accept both Loo-Macklin's brilliance and motivation other than the author tells us so. The final denouement when the alien gets Loo-Macklin to answer the question, "Why?" ends up feeling, although not quite as empty and trite as Alfred Bester's The Demolished Man, not much better, either. Without having critical insight into Loo-Macklin a great many of the choices he makes don't make a whole lot of sense, even in retrospect.
One final complaint: the plotting was a little TOO pat. Loo-Macklin has schemes within schemes within schemes and they all seem to work out perfectly. It would have been nice to once, just once, have seen his first plan fail and have backup plans come into play. It would have been so much more impressive if Loo-Macklin's final scheme were realized even in the face of errors along the way.