Where to start? It has taken me a while to organize my thoughts enough to write a coherent review. There were parts of this I liked and parts that I didn't and parts that were confusing. I really didn't even know how to rate this so I'm settling on the middle for lack of a better option.
First, what I liked. I liked Nyx. A lot. She is completely flawed, completely contradictory and made perfect sense.
"For eight years [I] lied to her with every breath, and now [I] hate her because she's deceived."
"But I was a girl who had broken her sister's heart and - for a moment-liked it. I had left somebody in torment and liked it."
"I think I'm wicked enough to love a demon."
I found Nyx entirely relatable. I'm not totally sure what that says about me...
...so we're just going to move on.
Nyx understood her duty (to die to save their world), but she sure wasn't happy about it. And who would be prepared to die at 17? And so she resents her father for putting her in this situation and her sister for getting to live a happy and full life while she can't. And her resentment and anger at her family in turn make her feel guilty. And I understood her throughout all of it.
Now for what I didn't like as much. There was an overwhelming about of mythology, myths, religion, etc. to keep track of. Some of these things were central to the story (and to understanding the ending), but there was just too much to remember. Which is why I think it took me so long to untangle my thoughts. I was trying to pull in and reconcile how all of these myths and stories were woven together and I was like:
The other thing I had a little bit of a problem with was the ending. Once you could understand how everything fit together the overall idea was neat, but in execution it didn't totally work (at least for me) because it kind of made the H and h into different people. They weren't the characters that I had liked throughout the story. They became entirely different. So it didn't really end up working for me.
"Everyone who ever bargains with me is convinced he is righteous...But you know what you are, and what you deserve. You lie to me but not to yourself. That's why I love you."