I've read this two times now (and a half, if you add up all the times I've been back to look at my favourite snippets. Of which there are a lot) and I loved it even more the second time, but I still can't formulate my thoughts into a coherent review. 
 I was sucked into the world(s) of ADSOM from the very first line - "Kell wore a very peculiar coat." By the characters and the storyline, but also by the amazing writing. Every paragraph, every sentence, every word built up the most vivid picture of the Londons, the people who inhabited them, their thoughts and actions and choices. 
 The characters are so very real, and flawed, that I couldn't help but love them. Kell, one of the two main characters, isn't particularly forthcoming and I've read some reviews who found him hard to warm to because of his reserve, but there's so much bubbling underneath, and he's got such a vein of sadness and anger running through him, and by the end of the book he was so tortured... As far as I'm concerned, he's simply the most precious darling ever to cross a page. Except possibly his brother, Prince Rhy, although he doesn't get a lot of page time in this first instalment. And then there's Lila Bard, who's simply incredible. Badass as hell, sharp and sassy and guarded and brilliant. 
 The book builds pace gradually, but I didn't find it slow at any point because the world was so mesmerising that I was simply dragged along for the ride. And as events take turn after turn for the worse, the pace and the tension and the action continue to ratchet up to the showdown - and just when you think it's over, no, there's more agony to come. The character and relationship development through the book was so understated yet undeniable, and what I loved most was the very real sense of consequences. The plot doesn't happen to the characters so much as because of them, driven by their - often very bad - choices, and their actions come back to haunt them and dog their steps at every turn. 
 If I had to criticise anything it would be that (on the first read) I was a little confused at the outset by the rules and reasons of the worlds, which were unfolded gradually, but they were explained soon enough. Some of the villains got a bit grandstand-y and cliched on occasion, although others (view spoiler)[ by which I mean Holland (hide spoiler)] were intriguing and dangerous enough to more than compensate and (view spoiler)[ I am very hopefully dubious that we've seen the last of him (hide spoiler)] avoided the black & white distinctions of good and bad guy. 
 In summary: a new favourite fantasy series, possibly of ever.