More of a 3.5 than 4. 
 Honestly I thought Cinder was just so much better than Scarlet. The main reason for that probably being I just didn't like Scarlet. She gave me no reason to empathise with or like her, so reading her chapters (esp at the start) was actually quite boring. That said, as it progressed and the stuff started happening I got to like her more. 
 Wolf. Um. No. I just can't take him seriously because of his name. I tried to get past it, but it's not happening. Wolf. Why? 
 The Cinder chapters were great though. Better than the first book, definitely. I loved her interactions with Thorne (and Thorne as a character) and Iko. They just kind of run around doing badass things and I'm 100% down with that. Also the lack of romance was actually really nice, although I don't mind the Cinder/Kai thing. 
 The Kai chapters. I liked them being there. I feel like I know more about him, and I like him more now. But can I just say idiot. 
 Ok so a few spoilers now 
 (view spoiler)[ I was genuinely shocked at Wolf. Did not expect. 
 I really liked the way Scarlet and Cinder are linked, and how they were uncovering the story at the same time, and you were learning with them and at different times and stuff. Well played. (hide spoiler)] 
 I don't have a favourite part, so I'll go with generally Cinder and Thorne and Iko.