I have not disliked a Culture book this much since the third one. While the premise is good, of "mirror universe" alien civilizations with Culture-level advancement but utterly retrograde philosophies they are able to make into reality on a terrifying scale, the implausibility of the Hells in the galaxy that Banks has created is illustrated by the extremely pat way they are ultimately dealt with and disposed of by the end of the book. Before we get there, though, we have to sit through lengthy expressions of an old man's obsession with eternal torment in the afterlife and (of course) sex, for narrative purposes that still remain entirely unclear to me. Also, why were two of the converging plot threads taken up by wisecracking, profanity-loving ships carrying female passengers with similar-looking inscrutable names? It led to much confusion and added nothing. This is what reminded me the most of the third book in the series, the visible spinning of Banks's wheels and recycling of ideas.