The characters' relationships change and grow in this book-- Grubb gets used to having a father, Cleona has a surprising relationship with Lorcan, and several of the characters have other identifities revealed. The watch Mack again plays a pivotal, if somewhat smaller, role in this installment, and sees some of his powers restored. Even Mrs. Pinch has some good moments of interaction with others, aside from her regular interjections of "Well, blind me!"
The use of Arthurian legend is somewhat like Salerni's in The Eighth Day, but with a Victorian setting. I can also see this being enjoyed by fans of Reeve's Mortal Engines series-- there are not that many books about flying building or cities, and the Odditorium is a great backdrop for this action-packed tale of traveling and fighting evil.