This is going to be an extremely biased review. Why? Because I actually wrote a spy-themed Cthulhu novel and am currently editing it. The fact this is something similar, though a completely different theme and style, makes me favorably disposed.
The Atrocity Archives is set in a world superficially similar to H.P. Lovecraft's Cthulhu mythos, only set in the present day and protected by a series of government conspiracies. These government conspiracies are not glamorous martini-drinking S.H.I.E.L.D analogues or even sinister X-files-esque conspiracies. No, instead, they're a bunch of bored civil servants smothered by bureaucracy.
The protagonist, Bob Howard, is more or less the opposite of your typical spy novel hero. He's neither suave, debonaire, or particularly dangerous. He is, however, frighteningly good at mathmatics.
Math is the basis of magic in the setting and the book is littered with complicated mathematical models which might or might not be accurate but blow my mind. Bob manages a comfortable everyman sort of hero and you believe in him as he struggles to be a field agent.
Indeed, what I like about Bob most is his unflappability in the face of mind-numbing horrors but complete bewilderment by mundane problems. Dealing with Cthulhu and Yog-Sothoth is Bob's job but the accounting department is beyond him. There's something to be said for being able to adjust to anything but your fellow humans and their trivialities.
Another thing I like is the book goes in unexpected directions. Without spoiling, the book touches on everything from Pulps to Norse mythology to what appears to sitcom romance without skipping a beat. There's few other places you can find Nazi plots, critiques on British CCTV spying, gorgons, and frost giants. The Atrocity Archives is divided into two novellas with separate stories and both are highly entertaining.
My favorite character from the book other than Bob is probably Dominique "Mo" O'Brien who is, ostensibly, the protagonist's love interest. Truth be told, I'm not sure if they're together or not since Bob is a bit of a nerd but certainly more effective with the ladies than most. Also, compared to some of his coworkers, he's positively James Bond. Whatever the case, she transcends this role in several places and is arguably a more interesting character.
I think the best element in the book, however, is not a character at all. The Laundry, the codename for the British department which deals with the supernatural, is an amazing creation. It manages to combine dull tedious bureaucracy, Lovecraft's abomination, magic, SIS, and pure insanity into one coherent whole. You could imagine working for the Laundry and it would either be deeply fulfilling or horrible beyond imagination.
In conclusion, The Atrocity Archives amuses me to no end. I am definitely going to check out the rest of the series and I recommend other people do the same. Just note that, occasionally, the technobabble gets a bit insufferable (especially about mathematics).
Buy at Amazon.com