I define a 3 star book as essentially one that is perfectly fine but I didn't particularly enjoy or connect with, and that is the case here. (Books I have a good time with get 3.5 or above.) I can appreciate that the author did some things well and I know there will be people that love the book. It just didn't work for me. 

It's a mix of portal fantasy and folklore - as far as I'm aware it's not actually a retelling of any fairytale, myth or legend, but it somewhat has the feel of one.  It's fast paced and does read quickly, but as a consequence I felt events were sometimes over with too fast. The worldbuilding was interesting but I would have liked a little more atmosphere. The central relationship between the sisters is one of the strengths of the novel. The villain of the story unfortunately felt more like a characature than a person. 

Overall I'm disappointed as I had hoped to love this book, but I do think that some people will like it a lot more than I did.