Is it possible to both love and hate a book at the same time? I think so. I think this book fits that description perfectly. I both love and hate this book. 
 First, I loved that Allegiant was told from the perspective of both Tris and Four. Because of the sheer magnitude of the story it is impossible to limit the view to one character. In the previous books, Tris is telling the story. You see everything from her perspective but in this book it seems important that you have another perspective. 
 I enjoy Four's perspective because in prior books he is this mystery of a character with real issues and feelings but because he's reserved and we the readers are trapped in Tris's POV; you really don't know what is happening with Four. He is experiencing changes in his life that effect him alone and yet we are getting Tris's assumptions on his feelings and half the time I believe she's as clueless as we are. 
 In this book, having Four's perspective means you get to see him working through the life changes he is faced with and how it affects his relationships with those around him. We get to see Tris and Four's relationship flex, strain and change shape through the eyes of the parties involved. 
 Having said this, there were times when Four's POV was far too similar to Tris's and I would have to go back to make sure I was clear who was speaking. But this is a frequent issue with books told from the perspective of certain characters. 
 Now onto second. The hate I feel is maybe not hate so much as confusion and turmoil. I do not believe the changes or solutions made in this book would create the effect the characters were seeking. But being as this is a work of fiction, I can accept that it is possible in this world Roth has created. 
 And then there is the ending which while I believe almost beautiful and necessary leaves me feeling a little lost. I kept expecting there to be another revelation, some solution, something. And yet the book ended and was final. 
 I have felt this feeling before. I have felt lost after finishing a series and I have to say that the few series's (this would be the third) are my favorite series of books. 
 This series is not only worth the read but worth the paper it is published on or the digital space it will take up.