This book was AMAZING! Bardugo has certainly outdone herself on this one. However, there are two things that I must say to readers going into this book.

1) PLEASE read the Grisha Trilogy and Six of Crows Duology FIRST. Although Leigh said that it isn't necessary to read the other Grishaverse books before this one, the reader will have a hard time understanding Nickolai, Nina, and Zoya's characters without having read those books first. In this book, not a lot of context is given to the characters and what they've been through...well, there is, but it's stated as a reminder more than an explanation. For instance, Nina's struggle with jurda parem is talked about as if the reader already knows what that drug is and why Nina had to take it.
Another thing is that King of Scars will give spoilers for the previous books. What happened with the Fold, Alina and the Darkling's respective legacies, Nickolai's struggle, MATTHIAS...etc. Also, characters like Kaz and the Jesper make for a few Easter eggs in conversation, so it's nice to know who they are.

2) Don't come into this book expecting a Nickolai "special edition" or something like that. Although Nickolai's story is definitely on the forefront here, an equal amount of time is spent developing Zoya's past, Nina's way of coping with grief, and the background of "The Cult of the Starless" (and really the story behind all the Ravkan Saints in general). But don't worry, Nickolai still gets his deserved page time!

Overall I will say that I really enjoyed this book, but it will really only be a five-star read to those who have read the Grisha Trilogy and the Six of Crows Duology. Otherwise...it may be too confusing to enjoy. It is so cool to see how Leigh has grown in her writing, from a trope-heavy Shadow and Bone to a roller coaster King of Scars. One minus was that the ending was a tinsey bit predictable, and I'm not usually someone who catches those sorts of things ahead of time. But perhaps that was just because it was what I wanted to happen...