I like this better than either of the previous books; the voice is just as strong, but Aaronovitch finally seems to be coming into his own as far as plotting is concerned. I'm also gradually growing more connected to the secondary characters, who are lightly sketched but in a way that accretes as the series continues.
I do want to file a "WTF?" about the back cover copy. According to mine, "At least he won't be alone. No, the FBI has sent over a crack agent to help. She's young, ambitious, beautiful . . . and a born-again Christian apt to view any magic as the work of the devil. Oh yeah--that's going to go well." This 1) is a baffling description of Reynolds, who is described as none of these things in text and seems to have no more difficulty with magic than anyone else (in fact, she takes it more calmly than many) and 2) seems like it's an attempt to imply there will be some sort of romantic tension between Peter and Reynolds, when there's nothing of the sort--in fact, given Peter's general propensity to hit on anything in a skirt, it's a little remarkable just how non-existent their chemistry is. Possibly of note, her description in-text is "thin and white," which may be the blurb writer's idea of beauty but has been pretty clearly established in the series as far from Peter's ideal. I have seen some bad blurbs in my time, but this is the worst in a while.