I'm giving it a 3 bc I know it's part of a longer series and maybe the rest of it will make this book seem better in hindsight. I love samantha shannon's writing but even so I was ready for this book to end. I need Paige to be a less stupid character and I feel like even the author forgot about a bunch of characters even though it was "Paige had forgotten" like I think the author literally lost her plot for some characters. 
Also every single conversation and experience is so freighted with meaning that it becomes exhausting. Halfway through I was like "just be criminals, quit trying to justify yourselves!"
Also  I do not like that she seems to drawing a false equivalency between Scion/Rephs and the syndicate/underworld, as if they are *equally* evil. Even in a fantasy dystopian version of London, that is a logical fallacy and it made it hard for me to read the book. 
I'm doing this as part of a read along so we'll see if subsequent books change my opinion, but for now it stands.