Okay, so a little cheating on the number of books, but each "chapter" in the Omnibus was published as a novella and it's my thing anyway so screw you.
Wool by Hugh Howey is fantastic. It shares a lot with the back half of "The Passage" by Justin Cronin by bringing to life a very dystopian future where post apocalyptic survivors huddle together in limited space. This time, it's in an underground Silo stretching over 140 feet into the earth. It's a great page turning read that feels ludcrous at first, but as Howey reveals more about the environment and how it got that way, it starts to become frighteningly real.