This book has the sort of thought provoking background that is the hallmark of good Science Fiction as well as a plot that keeps you turning the pages. Since I dislike reviews that end up giving away the plot I shall attempt to restrict myself to generalities. The book is essentially about the existence of parallel worlds and what the implications would be if we could learn information from them. The concept is not completely new - Keith Laumer's Imperium comes to mind - but Resonance is quite different in the way it handles the scenario.
In addition to its great background the book scores on the foreground characters and plot. The interplay between the hero and various almost identical heroines is extremely good as is the depiction of the hero, who for good logical reasons, is extremely introverted preferring to present the facade of a mute rather than expose himself to the ridicule that follows when the world has changed around him and he comments on it.
The book is set primarily in various versions of London in the year 2000 and the depictions of the every day minutiae of life are, I think, very well done and true to life. If there is one thing that is missing it is the Google search engine, which seems to be absent from the author's world view despite being something that was visible in this world's London of the year 2000. This may seem to be a curious thing to comment on but the plot does in part revolve around internet searching and thus it seems to me worth pointing out where it misses. On the other hand thought the problem of locating the needle in the haystack of search results is very well defined and other problems familiar to heavy internet users, such as finding apparently relevant documents in a language which you don't understand, do make their appearance and help (or hinder depending on your point of view) the plot along very nicely.
Due to the character of the hero there is none of the graphic and frequently gratuitous sex and/or violence that writers often use to disguise limitations in plot or characterization. The great thing is that this lack is not something you notice while the book is being read. There is plenty of action and intriguing plot twists but surprisingly very few loose ends by the time we reach the final denouement; as a result, while books in the same "universe" would be nice, a direct sequel seems unlikely. If there is one failing it is that I felt that the ending is a little too "pollyanna"ish given what we have seen before but on the whole I prefer this to the alternative of a depressing ending that wins awards but leaves the reader miserable.
All in all this is a book that appeals at many levels and one that will repay periodic rereading.