As Scalzi says in his afterword, this is a three-minute pop song of a novel, not a complex symphony. However, even the lightest of pop songs needs effort to make it work, and this does work on its own terms. It's a fun book that rattles along at a good pace, throwing enough big ideas into the mix to keep you reading and not asking too many questions about whether it all makes sense. Spends a lot of time setting up for not much plot, and relies a lot on coincidences to give the ending a personal stake for the protagonist, but does what it says on the tin and people who like this sort of thing will like this.