I understand why some readers have a problem with this book when they compare it to Divergent. 
 Tris and Four made decisions that frustrated me beyond belief. They kept secrets from one another even though it was clearly damaging their relationship and made them miserable. Tris wavered from being strong to over the top to almost breaking down, yet I could understand why. Clearly after the events at the end of Divergent she would be feeling insecure, scared and incredibly broken, so when you look at it from that perspective it makes sense that she behaved the way she did. 
 I really enjoyed the world building in this book, I didn't find it slow at all, all the things Tris pieced together were interesting and I really enjoy the world that's been created in this book. As for the ending...woah that throws everything off course. 
 So although I can appreciate why some people didn't enjoy this book nearly as much as Divergent I don't feel the same. The tone was very different but from my perspective it was fitting considering the events that were taking place.