Small Favor is, quite frankly, probably my very favorite book in the entire series.
One of the things that makes it really work is the villains. The Denarians are the featured villains this time around, making a repeat performance. For those not in the know, the Denarians are named for the thirty denarii that were paid to Judas Iscariot for betraying Christ. Each of the thirty pieces of silver has been cursed to hold the spirit of a fallen angel, and whomever possesses the coin is in turn possessed by the angel.
Of course, the nastiest of the Denarians are not those who are straight-up possessed by the fallen angel, but rather those who have entered into a partnership of equals of sorts with the angel; meaning that the host is so thoroughly nasty and villainous a person that the fallen angel respects them enough to work hand in hand with them rather than simply taking over and running the show on their own. This subtle little ploy by Butcher is an interesting one, and one that I happen to like. As nasty as the supernatural evil is that Butcher routinely pits Dresden against, it turns out that the very nastiest is simply human evil... albeit human evil that's gotten its hands on a fair bit of supernatural power to back it up. Nobody that Dresden has yet faced off again; the ghosts, the Sidhe, the Red Court of vampires, the White Court of Incubi/Succubi, the demons, etc. Nobody has been as thoroughly vile as the Denarians. And in this book, we really see their vileness.
That's probably what I also like most about this book; it really raises the bar. It is darker, more intense, and more desparate than any of those that preceded it, and at the end of the day, it left the main characters in a worse predicament, knowing that things were going to get worse before they got better yet. In that respect, it reminded me in many ways of the ending of The Empire Strikes Back; things are not resolved, and everything is just that much scarier.
Of course, the question remains; if Butcher is really only 50-60% through with the series at this point, how can he possibly carry on that level of intensity that he ramped it up to in this novel? Or can he? I don't want to spoil stuff that's coming, but I think he had mixed success with that venture in Turn Coat. In some ways, he let the tension slip a bit, yet in others, he kept it on and made sure that the situation generally devolved even more for Dresden. And it looks like, based on what little we know of Changes so far, that he's attempting to keep the pressure up still, as well as mixing up the format and formula of the novels a little bit. I'll let you know how well I think that works when it happens in a couple of months too.
Meanwhile, I picked up Mathias Thulmann: Witch Hunter to read next, which is an anthology of the three Warhammer novels about the titular character by C. L. Werner, Witch Hunter, Witch Finder and Witch Killer. Clearly Werner's strong suit is not the titles. In addition to the three novels, it also has three linked short stories thrown in to boot, so it's a nice anthology that offers up a little bit more than simply the three books slapped together.