This is the tenth Kitty Norville book, and is definitely not the place to start if you haven't read any of the previous books. So much of what happens in this book depends on the events of previous books that anyone who hasn't read the previous books is going to be hopelessly at sea.
Other reviewers have commented on the lack of a really effective 'bad guy', or even a problem to solve. I agree. The 'bad guy' for this book could have been omitted entirely without damaging the story - and, in fact, I think it would have been a better book if he had been cut. Most of the book was about the long-running series events, and the bad guy du jour simply wasn't convincing, or bad enough, to be really effective. The bits with him in felt more like interruptions to the plot than the allegedly major action.
We get a bit of Kitty's reaction to London - I liked those bits; she's a first-time traveller outside her own country, and that country is a young one. First time abroad, first time in a city with so much history. Others have commented that there wasn't enough London-specific scene-setting, to make it clear that Kitty was in London rather than some other city, but I didn't feel the lack. To be fair, in most books cities come across as pretty generic unless the action is centred around a famous monument - and there's only so many ways you can do that without being contrived. Besides, it's supposed to be urban fantasy; if you want a detailed description of London, buy a Lonely Planet guide. (However, American authors please note: British people do not talk about 'blocks'! Most of our cities - as Kitty notes - are not planned on the grid system, so we do not use the 'block' as a unit of distance because it doesn't make sense. We use metres or yards, or say things like "Turn right half a mile before you get to the cinema that was burned down three years ago.")
Character-wise, we see more of Cormac. I think Vaughn is setting up something special with him and his ghostly passenger; this is a good thing, because Cormac - no longer the gunslinger he was - is a bit a of fifth wheel at the moment. He needs a new role, and Cormac's bits indicate that Vaughn is going to give him (them?) one.
One thing I like about Kitty is that she is not like practically every other urban fantasy heroine. She is not some badass ass-kicker who can knock seven bells out of anyone who gets across her, without smudging her makeup. She's an ordinary woman caught in big events, doing her best to do right by the people who depend on her. She's got real courage - the kind of courage that means you don't back down from what you know to be right, even when you're scared. She's going up against beings that could rip her apart, and pretty much all she's got is a good line in fast talking and the ability to fake it really well. She'll fight, but only as a last resort. She might not be the kind of larger-than-life, flashy heroine we're used to, but she's very human.
Ben, her husband, is the kind of quiet, supportive partner that it's realistic for Kitty to have. Kitty's the more outgoing of the pair, but she'd be squashed by someone more 'rough and tough'. This series isn't about sex and lust and emotional upheaval, so if you're looking for bodice-ripper/chicklit disguised as urban fantasy, this is not the series for you. Kitty and Ben have a loving, stable relationship that sustains them for, not distracts them from, what they have to do.
All in all, this book has the feel of a book that is setting up something bigger further down the line.
On the bad side, this meant that there wasn't much in the way of suspense - it was mostly jockeying for position in the series events - and the villain du jour was a bit of a failure.
On the good side, it was an entertaining read, and Vaughn has moved some characters to where they need to be for the events of future books.