This is a fascinating, well-written, thoroughly engaging and original novel. While there is a crime basis to the plot, it is fundamentally about the characters, and about philosophical detours. As such, it is a book to be read slowly and savoured; it does not have a great deal of action, but it does hold your attention.
Zeh has an eye for seemingly unimportant detail. Her description of Rita, for example, is a joy to behold; a maelstrom of ticks, observations, quirks and minor details that somehow coalesce into a vivid picture. For the most part, each of the characters in the book are singular (i.e. they don't start resembling each other - a common error) and interesting.
The plot itself, viewed after finishing the book, is not all it might be; there are some practical flaws that could be argued by those who like a nice tight, compact storyline. But this book isn't about the plot - it's about the slightly loopy characters and the strange way they deal with leading a life.
All in all, this was refreshing for its originality, its willingness to engage in erudite but clearly-explained scientific arguments, and for a quirkiness that manages not to jar. Thanks to Amazon reviewer RachelW for pointing me towards it.