Perhaps my previous experiences with Nix's writing were from a more youthful point of view, but I could swear his new series, Keys to the Kingdom, is aimed at an audience that is more appreciative of the fantasy genre. Judging from the first book, Mister Monday, I would recommend it for the young and very young of heart.
Although a fast-paced page-turner, this book would have been better off without some of its fun little quirks. For example, the attempt to lure in a more profitable consumer is ruined as Nix tries to simulate teenage chat speak in an e-mail between two characters. He slaughters the use of acronyms and makes young adults cringe at his shorthand. The action-packed conclusion was somewhat ruined by over-explaining the events to an underestimated reader. The result involved several yawns during the climactic duel between the protagonist and Mister Monday himself.