For a Cambridge Companion, this is surprisingly shallow. The other reviewer pinpointed one of the faults of the book; but the chapter about Religion and SF by Mendlesohn is also quite poor. A discussion about religion in SF in a book printed by such a prestigious press which does not mention James Blish's A Case of Coscience? I can't believe it. It's like a book on Renaissance Revenge Tragedy which doesn't mention Hamlet. But what might be even more disappointing is the absence of Philip K. Dick. Of course the author of the chapter is allowed to devote more time to what authors she thinks are more important, but since this is a book that should help students to understand what is sf and what are its most important works and issues, the fact that such novels as VALIS, The Divine Invasion, Radio Free Albemuth, The Three Stigmata of Palmer Eldritch are not mentioned in the context of a discussion of sf and religion is bewildering.
All in all, my very personal opinion is that some parts are quite good (McLeod's chapter on politics, but also Butler's on sf & postmodernism and Wolfe's on sf editors), but some are awfully poor and poorly researched. And this should make us ask why did the editors chose those authors for those chapters, which is a question that directly leads to another, why haven't some very important scholars been involved (no, I won't drop names, but anybody who's knowledgeable with sf criticism knows what people I mean). Once again, the editors are free to choose, but then they're responsible for their choices, which are puzzling at best.