In case you missed them:
I finished this book a while ago, and honestly don't remember that much about it. I apologize for the seemingly short post, and I'll try to post more quickly after I finish my books so that I can go more in depth.
I do remember enjoying this book much more then I Am Number Four. I thought the story was better, and I liked the other characters more than I like John/Four. Seven was very interesting, and I'm glad we were introduced to her in this book. And learning more about Six was also nice, although I wish there would have been sections from her point of view.
I did not like that John really didn't mature much from the first novel. He was still annoying and self-centered, and even though he tried to be the good friend and not meddle with the girl Sam was falling for, he still somehow managed to muck things up. Oh, and the whole Sarah thing was strange and fast and not really explained well. I know he wanted to see her... but still.
I did like the ending though, and I will probably read the rest of the series to see what happens to the remaining Garde. I'd give this book a solid 3/5, and would recommend it to anyone who has already read I Am Number Four. And if you've seen the movie, but haven't read the book, go read both books now. They're much better.