I haven't enjoyed a book this much in a long time. After a few pages I already knew that this would be one of those books I'd stay up for until 5 AM to finish it.
Hugh Howey is an excellent writer. His words are gripping, his descriptions sharp and his dialogue is some of the best I've ever read.
Take one underground silo, a hundred floors (no elevator) and a forbidden, poisonous outside. The worst punishment is being sent out to clean, a death sentence. The offender gets an airtight suit, limited oxygen and gets send outside to clean the cameras which project the view of the outside on to screens in the upper levels of the silo. Eventually the oxygen will run out and the cleaners die.
To sum this book up: Dystopian, post-apocalyptic and simply perfect.