I should say right away that I'm rating this book as a children's (middle grade) book, not young adult, which, I think, it's theoretically supposed to be.
It didn't read like YA. It read pure middle-grade to me, right down to Emilie, the heroine, coming off far more as 12-14 than 16 which she was supposed to be. The writing style, the plot, the occasionally unnecessary explanations to the reader - all that felt "young" to me (with the possible exception of occasional references to prostitutes
That said, once I'd adjusted my mindset and read it like a children's adventure instead of young adult fantasy, I really liked it. It reminded me a lot (in the general sense of wonder and adventure) of Jules Verne's work or Conan Doyle's Challenger books, although it was set in a fantasy world, not "our" world (one rather like ours / sort of 19th century feel, just with magic). The pacing was good (at least I didn't find it dragging), the adventures exciting, the heroine spunky and feisty and brave while not being superpowered, the supporting cast largely fairly good.
I'm not entirely keen on the hint of Emilie/Daniel we got from this book (I take it that there are more planned, although this works very well as a standalone), but, eh.