This is the second in a duology (first was Six of Crows) I started a while back. When I picked up the first one, I didn't realise there was another trilogy of books set in the same world, so I went back and read those in the intervening space, to get a better understanding of the world. It's not essential, but I'd recommend the trilogy first if you are going to look into the Grisha world. I really enjoyed all five of these, despite reading them in an odd order. It was an interesting premise for a Fantasy world, and I do think that YA writing is very strong these days - makes me wish I was a YA again - ok, not really. Just makes me wish we had books like this in the days when I was. I love the outcasts and rebels in this pair of books and overall, probably like them better than the Grisha trilogy, which is a bit more serious.