Writing Urban Fantasy isn't easy these days. The formula has become rather predictable. In fact, that's the main reason I've avoided the genre entirely myself as an author hithertonow. It pays well, and books that do well in this field can be quite successful, but I mean, how many different ways can you write about vampires, fairies, mages and werewolves?
Well, in this book, Jim Butcher found a way. Basically, he takes a random grab bag of about six different kinds of werewolves and half a dozen types of vampires, weaving the different types of cinemea and mythology into a believable mix. When an author makes up a setting, they can sometimes fall into the trap of "the Seven Stones of Power" or the like, in the sense that it seems more like a role playing game setting designed to make as many character selection options as possible available in chargen. On the other hand, sometimes a world can seem awfully...empty. The real world has hundreds of different cultures, religions and languages that all conflict with each other, which is why the real world often comes up with ideas that an author couldn't conceive of in their wildest dreams, despite being able to ignore things like the laws of physics.
Butcher's setting really sings. It fits quite nicely between the semi-formulaic intro book, and the 'all hell breaks loose' of the following book. He gets a few allies, advances a few relationships, and sets the foundations for his own destruction at a later date. In short, I suspect that Butcher didn't even know how good of a foundation he was laying for his later books when he wrote it.
The book is basically about a series of murders Harry has to solve for his Police contact, which happen to involve obviously canine involvement. He has to navigate through several different suspects and figure out which is which. That, on top of everything else, makes it particularly interesting, since it has an actual mystery that follows its own rules quite well.