I spent a whole day reading this book until 1am of the next day. It was that good.
The FMC. Kayla was interesting, first a princess, now a slave, but she keeps her pride and her attitude. Very good. What I didn't like was the sudden change from "Zayn must be kidding, he can't be my mate!" to "I must find a way for him to want to stay with me". She hated him, but then she wanted to keep him. There was no process, no falling for each other. Just sex and then more sex.
The MMC. Sixx was awesome. A person who was recently "cursed" and can't enjoy that what he loved before: drinking, whoring and fighting. He has a powerful presence during the whole book, and his struggles with what he was before and what he is now were heartbreaking. He is the character that developed the most, and, I think, the center of the whole story, no Kayla.
Zayn. There is not much to say about this dragon. She is part of Kayla, but she doesn't share her abilities unless she thinks it would be help her find her mate. Kayla has never taken the form of a dragon! I simply didn't like Zayn. The others dragons at least had a personality; she doesn't.
All in all, the book is good, and there are a couple of surprises allong the way that make it worth it. Poor Sixx, he receives the most.