The only reason this is getting 3.5 stars is purely a matter of preference on my part - the book is good and anyone who liked the other ones so far will love it!
It's just I don't care much for multiple POVs - I know, inevitable with all these characters, and I even wanted to know what was going on with all of them! - but every time I really started to get into someone's story the book would switch to someone else.
I need to be really invested in the characters for a story to work, and I was fairly invested in most of them, due to the previous books, but it was still frustrating!
So let me go more into each character in the story:
Cinder - I really like Cinder and, obviously she wasn't in the book as much as I wished her to be, since it was Cress and Thorne's book, but even so there was so much happening in her story! Too much! Because I felt like we never really got into what she was really feeling about it all. We were told how she was feeling which... is not the same thing.
Kai - I am sorry but he is boring, dumb, and so far mostly useless and I can't, for the life of me, even remember what Cinder saw in him.
Iko - Barely there comic relief :(
Scarlet and Wolf -
Thorne - Whenever we started going a bit deeper into his character, the POV would switch. Luckily, I really liked him from the previous books, otherwise I would have ended up giving up on this book.
Cress - I LOVE Cress! She deserved a book devoted to her, and I mean really devoted to her, not as this one was. Still, she was the most developed character in the book, as she should be. And I loved it, she was a whole deconstruction on the damsel in distress, the willing damsel in distress, because she wanted to live life the way she'd dreamed it, and even when things didn't go her way, she just adapted her dreams to fit. And I think that's just as powerful as the more usual strong female characters: one who dreams of being the princess waiting for her prince in her story and sticks to it, because that dream is as valid as the one of being the lady-warrior who saves the world.
The other characters were barely there, and were mostly clichés of incompetence (Torin), or wise mothers (Priya), scientists who were ~evil~ but are now redeemed (Dr. Erland), and evil because she's evil Queen Levana.
That is not to say this isn't a good book, I know I repeat myself, but I must.
I read it all in one go, it's extremely addictive, it moved the plot along, you got to see all of the characters, and no character was badly written.
It's just... at 560 pages, I wanted more...