The book was ok. TBH as I write this about a week or so after I read it, I've forgotten quite a bit of it. I'll be honest, I'm a little troubled by some of the analogies that come naturally due to the Russian based fantasy world. The Darkling, and major villain, becomes a Stalin stand-in. And while I don't think communism, especially under Stalin, was good for the people of Russia - I also don't think the right answer was a return to the monarchy, which is what this book says.
It's good YA, but not great and memorable YA.
The novel also upholds the idea that the monarchy is a good form of government, and that's a pretty old and un-examined fantasy trope. Yes you have an abusive monarch who is overthrown. But the overthrowing of the monarchy is negated by the fact that the country goes back to the monarchy at the end, indicating that the problem isn't with the monarchy but the person in that position. And that is a little troubling.
Also, reading the one star reviews from Darkling fans will never, ever not make me laugh.