My full review is here on my personal website. I'll post a few excerpts here, though:

5.0 out of 5.0 stars

The very worst thing about this book is the simplistic way that certain things have been lost. I can understand the Builders having not allowed certain things into the city, but to keep the very important lockbox secret? What?! If I were to have built a city for this purpose, the “very important lockbox” would have been a “very large and centrally located safe” with some simple design/camouflage to prevent people from trying to force it open too soon.

The very best thing about this book is the city, the people, the mystery, Lina, Doon, the pipeworks, the- Well, take your pick! I can’t tell you all of the great elements existing in this book without reading the book to you! Even that “worst thing” was a necessary for the story to exist at all. ^_^