Lina and Doon, both winning characters, are back front and center, and most of the other characters are peripheral, some so much so that one might wonder what they're doing there. In fact there's an entire subplot that could be removed from the book without any loss of sense or pleasure. But Ember itself is as fascinating as ever -- there's just something about an underground city, even in the dark, that haunts the imagination. Author Jeanne Duprau also has a talent for observing the nitty-gritty details while imagining her way into the lives of her characters, using sensory description in a way that is, even in the midst of a post-apocalyptic sci-fi tale, intensely realistic.
DuPrau has said that she never planned Ember to be a series. No kidding. While book 3 seems hardly to belong to the series at all, the others do at least follow a chronology, though they are very different. Book 1 combined adventure and philosophy, while book 2 leaned more heavily on the ideas and allegory, and less on the action. Now the series wraps up with a book that is closer to a pure adventure, though still with a few interesting ideas floating around. For series fans it's a treat, in more ways than one, and ends in a thoroughly satisfying and hopeful way.