I really wavered between giving this 3 stars or four...Largely because of one very poorly developed character that kind of ruined a large portion of the book for me. Evan Walker. 
 When I started out reading this book, I really liked the main character, Cassie. She was a well-written character, a teenager trying to survive in a post-apocalyptic wasteland entirely by herself. Her backstory was interesting, although the way the author wrote her to be kind of baby-crazy was a little obnoxious. When we're introduced to Ben's part of the story, the excitement starts to pick up even more. Here is where I can see why people are comparing this to Ender's Game. Ben's pieces of the story are definitely reminiscent of Card's famous novel. 
 Everything seems to be going good, I'm really enjoying the book for the most part, and then we get to Evan Walker. 
 Most boring romantic plot device ever. 
 His romance with Cassie is bland, uninteresting, and downright stale. Its not believable by any stretch of the mind, its out of character for Cassie, and she trusts him FAR too easily for my taste. The entire stretch of the book where she's with him in the cabin remind me, quite painfully, of crappy fan fiction I used to write with my friends in high school where we'd stick the characters in a cabin in the woods for absolutely no other reason than that it makes the perfect location for cheesy, poorly written romance. 
 In fact, this section of the book feels like it doesn't really belong at all, and is without a doubt the most poorly written part out of the entire novel. At first, I thought it was Cassie's fault. I felt like her character had suffered a dramatic change and started disliking her greatly. I'd speed-read through those parts just to get back to Ben and the real action. It wasn't until I was almost done with the book that I realized it wasn't her at all. It was Evan. 
 He is so poorly developed, its ridiculous. He practically has no character at all. He's a blank-slate stock character stuffed into a story that was perfectly fine without him for the sake of a plot device, with absolutely no other purpose aside from an awkward romantic interest and a tool to further the plot. He could probably be yanked out of the book and replaced with a lamp and there wouldn't be too much difference. 
 The only other major issue I have, however, is a very small part in the beginning, and I'm probably the only person it bothered. (view spoiler)[ Its the scene in the woods with Crisco, where he tries to rape Cassie. The scene is disturbing on its own, but what really made me want to vomit was the way his actions were completely excused by the author because he misses his parents. Boo-fucking-hoo. The icing on the cake is the line "You wouldn't have hit me if you were a virgin". I'm sorry, no. Vomit central. I actually had to put the book down and take a break from reading it for a few days because I was so angry at that part. (hide spoiler)] 
 While I enjoyed this book overall, the abysmal way Crisco's scene was handled, the fact that it didn't add to the plot and didn't have ANY purpose whatsoever, and the trainwreck that was Evan Walker's character, or lack thereof, really makes me struggle over giving its four stars. I think I'd have to give it 3.5, because for its flaws it was a really exciting story, well-written with the obvious exceptions, the parts without the crummy romance kept me reading obsessively, and I'm really looking forward to the next book. Rick Yancey certainly isn't the worst YA writer I've seen (that award still goes to Stephanie Meyer), but he has a lot of room to grow, and I look forward to seeing if and how he improves in the future.