No Rest for the Wicked was a bit like trying a new fairground ride for me. I went into it doubtful, to be honest, not due to any presupposition about the author, but because I've not enjoyed my forays into supernatural thrillers/horror before. The premise is a touch B-movie (not that this is necessarily a bad thing) with the use of a supernatural force in the form of angels—but not as you know them. These threatening figures are partly rooted in religion and partly in science, which is a wonderful balancing act and helps to lend the book a sense of ambiguity, and it's uncertainty that kept me off balance as I read. The encounters are suitably grisly, the sense of threat is near-constant, with that classic dread that comes from Cobain having an unstoppable, implacable monster in his employ. It's a personified threat, to an extent, but it's nonetheless uniform and total in its effect on the world.
I found the sub-plotting of the principal characters to be useful but somewhat underdeveloped, by which I mean that the human, personal story functions well mechanically—it's vital for the plot and contains a well-used but very satisfying twist—but I do feel that the drama and the depth in the relationships could have been built far higher. This probably would have added a good third to the length of the book though, so I can understand why this might have been sacrificed for the sake of pacing.
Without giving anything away, the denouement is delivered very capably, in a manner that I couldn't predict, somehow fulfilling the character arcs well while still making sense in the world of the story, rounding off the author's exploration of the themes of morality in a way that echoes the theological dichotomy of law and grace—though I'm nearly certain that this is my perspective rather than an intended reference.
In all, the book manages to be respectful of religion, which can't help but be a major element of the story, whilst also being critical and subversive with its ideas. I recommend that you satisfy your curiosity if this book has taken your interest.