I enjoyed this book, although I think I might have enjoyed it more had I read it before Bardugo's other series. She's a more assured writer in the next series and the maturity shows in the characters she handles, the complexity of the plot, not to mention the morality.
Which is not to say this wasn't a good book. I really enjoyed it and the world that Bardugo has created is exactly the sort of epic fantasy I enjoy.
[spoiler]I should have seen the Darkling coming and I didn't because I am so used to the "ancient powerful being falls for self-conscious teenaged girl" trope, especially in YA, that I didn't blink. And, I admit, he had something of Loki as played by Tom Hiddleston about him. But I was delighted when the story actually took a "who are you kidding, this is not how it works!!" approach. A+ on that![/spoiler]