This series has turned a corner and become more serious, with this volume. Or the author has decided to take it more seriously. I don't mean it's stopped being funny; it's still Bob's irate-nerd edge-of-over-clever voice narrating, and that still turns the pages nicely. Nor do I refer to the escalation of the story arc, which is indeed escalating (The Stars Are Right, more or less now, as of this volume).
No, I mean that the early volumes were gonzo horror, starting with Nazis From Space, more or less literally. The set pieces were genuinely spooky, but shallowly so; monsters and mind-invading demons from beyond space and time.
This time, the on-stage threat is an American televangelist. There are of course monsters and mind-invading demons lurking behind the plot curtains -- but the televangelist and his thoroughly-human brand of evil grounds the story, in a way that I don't think previous volumes managed. We start to see what occult threats mean to civilians, to us; not as a hypothetical future catastrophe, not as cinematic heroes-vs-goons bloodbath, but in lives ruined and destroyed.
(Well, I should say, as that and the looming planetary catastrophe and the cinematic fight scenes. Each at appropriate times in the story.)
Also: the author has some words for American fundamentalism. He's not saying that the real-life Christian megachurches want to summon Cthulhu and destroy civilization... but Lovecraftian horror is big on religous cults, and Stross isn't shy about pointing out how close some popular religious movements are to cult-land. The repressive, controlling, (...sexist, anti-intellectual, power-hungry, self-righteous...) elements of the religious right are the explicit villain here. The monsters, to some degree, are just reification.
(Just last month I was reading -- thank you, Fred Clark -- about the five points of Calvinist theology. But it had not occurred to me that if you start with a classic Lovecraftian cult story, all over people going hopelessly insane and corrupt bloodlines coming out to overwhelm them... well, those five points wouldn't seem even a little bit out of place, would they? No, they wouldn't. Thank you, Charlie.)
I don't want to give the impression that this is a Message Book. It's the same thriller ride it's always been, with plots and horrors and spies and stuff. I'm saying that the tone-tension used to be between cosmic horror and petty bureaucracy. But the petty bureaucracy is slowly revealing itself as the high-stakes game-playing of serious espionage; the tension is now between cosmic horror and real-life horror. I don't know if Stross intended this curveball from the beginning (I doubt it, really); but I like it.