There is 1 reason why I've given this 3 stars instead of 4. This should not be a series. 
 It was so perfect as a stand-alone and honestly I don't see how adding another book can do anything other than ruin it. 
 This makes me sad because I love the structure of this book, the pacing was engaging and there was always something going on. I loved seeing how Em and Marina are the same and yet so different, how Em and Finn deal with facing their past. The ending was a little weird, I understand it...but feel that the very last part where Em wakes up wasn't necessary, I would have almost preferred it to have been left more ambiguously.