Fantastic, in every sense of the word. Fantasy fiction fans will love this book. 
 My take: 
 Where to begin? Perhaps with the idea. The idea behind this book is intriguing and elegant. Schwab describes her three Londons, each in their own sealed pocket of reality, with an admirably confident and consistent logic which carries the reader between them smoothly, letting the characters take the knocks. 
 Then the characters. I liked Lila, and was interested by the rest of the cast, but the most important character here is Kell. Other authors give us all-powerful sorcerers, but Kell is a vulnerable magician, and it is this vulnerability that draws us to him. After all, if someone can't be hurt, can't shed blood, it's hard for us to worry about them. And my goodness, does the blood flow in ADSOM. If you have an active imagination and haemophobia (that's right, I Googled it), I'm not sure you could handle this story. For the rest of us, the gallons of blood just add to the slick sheen of the tale. 
 The plot is a good combination of adventure, betrayal and loss which glides along at pleasing pace. 
 In short: this is the first book in a long time which has kept me up reading past 2am because I did not want to put it down. Read this book. Then groan in frustration that we have to wait for the next in the series.