I loved this book. Marie Lu's world building is fantastic. I actually felt as though I was inside the world of June and of Day, and I could see the streets and the JumboTrons, the police and military. But what I loved most about this book was Lu's characters.
I'm a sucker for well-rounded characters. If I love the characters, I read the book. Day is pretty much a badass in every thing he does. He's smart, quick, and if I were to watch him fight, I could picture him as a Jackie Chan or Jason Bourne. His sarcasm mixed with his kind and caring nature makes him a solid protagonist to follow. He's likable. Very likable.
June, on the other hand, is the opposite of June, all though she still a likable character. Grown up under a brother in Military, she is all about the Republic and doing things for her country. But she, like Day, is also quick and smart. She's the military's Prodigy. And when June and Day cross paths for the first (technically second) time, obviously sparks fly.
But for me, the sparks flew a bit too quickly. I understand for the purpose of this story there had to be some romance or love interest. But there wasn't enough tension between the two to really believe it. I needed more from them, more spark. More intense moments. More heartbreak.
The other thing that bugged me was that it was a bit predictable. At least for me, I predicted the ending at least a few chapters in. But I held out, hoping I was wrong, and by the end of the book I was reading for enjoyment to the point where I didn't care if I was right. Lu's action sequences were heart pounding, and I turned each page, my head deep in the book, picturing everything that was going on. I was in the action as Day or as June. I could see it as I read it.