I could not put this book down! 
The main character was beautifully written. A true morally grey character that came off as complex and layered, without being forced or over-the-top. The themes of the book were masterfully and subtly showcased through the plot lines and the characters' choices. We're introduced to a very cool worldbuilding that was expansive without being dispersive, with very authentic and enchanting Celtic folklore that felt very much like an old, oral-tradition fairy tale.
I'll definitely read more of this author's books.