The Nightmare Stacks is the seventh novel in the Laundry Files series by Charles Stross. I've been reading the series since the beginning, and enjoyed it all. This latest entry is no exception.
In the early novels, the story mostly followed Bob Howard, a Laundry agent with a talent for getting involved in sticky situations. Later books have moved on to focus on other characters, though Bob and other characters from the earlier books are mentioned quite a bit. The Nightmare Stacks is told from the viewpoint of a PHANG (basically a vampire, though not quite like the stories) Laundry agent named Alex. He's pretty much a stereotypical nerd - high math skills, social ineptness - until he contracts the PHANG syndrome and is dragged into the Laundry world. Much of that happens to him in The Rhesus Chart, the fifth Laundry Files novel, where Alex is a minor character.
The story in The Nightmare Stacks starts with Alex trying to get acclimated to his new life as a Laundry agent, while at the same time dealing with family issues and trying to overcome his own insecurities (mostly with regards to dating). The first third or so of the story moves a bit slow, in my opinion, but it's all good groundwork. Things really pick up when there's an invasion by an extra-dimensional force, and Alex is the man in the center of the action. It's no surprise that he ends up finding a way for things to work out, but the journey there is a lot of fun.
At a high level, the plot bears more than a passing resemblance to Terry Pratchett's Discworld novel Lords and Ladies. The similarity is only at the very highest level of the plot - just about every detail is significantly different - but it's still pretty clearly meant (at least in part) as a tribute. In fact, Stross dedicates The Nightmare Stacks to Sir Terry: "In memory of Terry Pratchett, who showed us how it's done."
One of my favorite things about the Laundry Files novels are the way that Stross captures the frustrations (and occasionally advantages) of working for a large bureaucratic entity. I've never worked directly for a government bureaucracy, but I've consulted for a few and worked in large private-sector organizations that have many of the same traits. The Laundry agents have to deal with paperwork, regulations, office politics, unwieldy training schedules, overbooked calendars, and all the other things that can make life in a big organization such a exercise in frustration. It all sounds dull, and it certainly is if you have to live through it, but properly described in a novel all that bureaucracy becomes a living part of the characters and story that those of us who have experienced it can identify with strongly. Stross makes it work as well as any author I've ever read.
If you liked any of the other Laundry Files novels (particularly The Rhesus Chart), then The Nightmare Stacks is definitely for you. I certainly enjoyed it as much as any of the other books in the series.