Interesting thing about tight first person point of view: when the main character feels strongly about another character, it comes through really strongly. Take for example Christy, Adam’s ex-wife. On one hand, I’m sure she’s not quite as bad as she appears, given that all we see is from Mercy’s point of view. On the other hand, she’s really a fairly troubled person.
On the supernatural scale, we actually manage to step up another level from the River Devil and Coyote and friends. This time around we get an ancient big bad from the Canary Islands who’s just as hard to kill as the River Devil but has even more firepower (heh) on their side. It’s a fascinating bit of mythology I’ve never come across anywhere else and manages to fit well enough into the current world.
One downside of amping up the big bads like this, is it’s uncertainly how much further than can go. Many urban fantasies have this problem. Well just have to see how Briggs handles it. Luckily, all of the current danger–despite being ancient and terrible–has been relatively constrained geographically. If I were a betting man (or reading the blurb for Fire I would bet that we’re going to get a much larger scope next time around.
One final note, the romance aspects of the books are getting more and more frequent as we move along. There’s still little enough explicit, but it’s been drifting more and more each book.