I really dithered over whether to rate this four or five stars. In many ways it continues the excellence of Divergent, but I think the sheer number of times I wanted to scream 'What are you doing???' to Tris probably means I have to deduct a star. Don't get me wrong - everything that was great about Tris in the first book is still there, but she does have her frustrating moments, in particular with her reluctance to talk to or trust Tobias/Four fully. Once or twice, fine - but repeatedly? 
 (view spoiler)[The scene where she promises him she won't hand herself over, and then goes and hands herself over was one of those scenes where you can understand on an emotional level what she thought she was doing was right - she was trying to save lives, but as a Divergent to three factions including Erudite surely she had to realise that her giving them access to her brain was potentially fatal to everyone anyway? I think that's the beauty of Tris though - she isn't perfect and she makes mistakes (and she makes a few of them in this book) but she learns from them, thankfully and grows. A lot of times it would have irritated me to see yet another self-sacrificing heroine, but this was based on more than her needing to be a hero. For much of the book she's fuelled by guilt and the need to atone for killing Will in the first book and Four tells her more than once that she has to start looking after herself and it takes her almost being killed in the compound for her to realise that. (hide spoiler)] 
 It was great to get some background on the factions and the amount of action was certainly welcome. Too often the 'middle' book is about getting characters in place for the finale, but this one actually managed to do that while telling a really good story and providing some action - more than I thought we would get. Mostly it was great to see the character growth that happened - everyone becomes more rounded and the emotional conflict feels believable. Four and Tris have their issues as a couple because they are rubbish at communication, Tris and Christina go through a lot of the book because of hurt feelings, there are lies and anger and emotions flying around all over the place and with every one of them, you could take away the setting from the book and apply it to any number of real situations. Who hasn't had a fight because they've kept something quiet? Who hasn't made a wrong choice, or felt guilty to the point of it becoming destructive? It's real feelings in a strange new setting and it is one of the strengths of this world. 
 All in all, it was a great book. I may go back in a couple of days and bump this up to a five, but for now I will say it's a 4.5. I just want word on when we can expect book 3 now! It can't come soon enough.