Liminal by Raphael Ness

Neil Beckett knew he was dead. But he found himself in a strange place, and not the afterlife he was expecting. Every day is the same, except for the days when something changes. With no guidance except a vague note, Neil is determined to beat the Devils in Charge of the run-down institution that he found himself in at their own game, and earn his way back into the afterlife that he was expecting. If he can survive breaking the game and being hunted, that is.