Warning: This book will make you cry. I've read many books that have made me tear up a little, but I haven't really cried while reading a books since Harry Potter and the Deathly Hallows (and really, who didn't cry reading that book?) 
 In the beginning you have your typical mean girls. Sam is not the most likeable character. Her typical mean girl behavior makes you want to smack her upside the head. She treats people like crap, and laughs while doing it. In some of her inner thoughts she knows it's wrong, but follows her friend Lindsay anyway. 
 After waking up on the second day, after appropriately freaking out, she makes only small changes. It's not until the third day that she realizes that it might not be about her... 
 As she lives each day over she makes changes trying to fix things. She makes new friends and new discoveries that change her. She starts to fall in love and really care about other people. She progresses from all about me to what can I do to help her? 
 Day four was my favorite of all the days. She said what she thought and did what she wanted, knowing that it would just repeat again tomorrow and all would be forgiven. (It was especially gratifying where Lindsay is concerned). Day seven was also really good as she went about fixing things for other people. 
 Lauren Oliver is a fantastic writer, she really brought this story to life. And even though it'll probably make you cry, it is well worth the read.