** spoiler alert ** 
 In general this was a good book, and there were times I just couldn't put it down. For instance, when Lena and Julian are in the old subway, and are saved from the scavengers by the then-mysterious people who apparently wield rats. "Oh my god, what is this? WHERE DID THIS COME FROM?" I thought. There are a few things I think could have been expanded upon to make it better, though. For instance, we have all this build-up with the parallel stories, but we don't get much background on how they came to the decision to stay in New York and scout out the DFA. 
 We also don't see a lot of interaction between Raven and Blue until they're migrating in the Then storyline and Blue is dying from sickness. We do get the background of how Raven found her, and it explains why Raven joined the invalids and why Blue was so important to her. But for a group of people who live in the wilds because they want to be able to freely express emotions, including love, we don't see a lot of affection. It is, perhaps, against Raven's character, but with how much she freaks out at Blue's death, I would've liked to at least see more interaction with them. 
 One final thing, and this is completely subjective, was that I didn't completely enjoy the ending. It was a good turn of events, but I feel like even if it's a series or trilogy, long novels like this shouldn't end in such cliffhangers. I felt the same with Crescendo by Becca Fitzpatrick, actually. We know the story's not done, you don't need to do something like that to us! 
 But, despite all this, I did rate the novel four stars, so it's definitely a must-read if you enjoyed the first book.