I actually ended up really liking this book a lot. Totally fun. The first 25% or so dragged so slowly for me. I couldn't get into the characters and felt that the plot was winding all over the place. As soon as the author gets back into the meat of the overarching mystery/conspiracy though, the pace picks right back up again. From the second Tris surrenders herself to Erudite to keep other members of Dauntless from being remotely controlled, I was on board again. The plot and action are much tighter from that point on.
Tris also continues to be a pretty cool protagonist.
The big reveal at the end made me raise an eyebrow though. Hmmm, Reavers? Anyway, I'm having fun theorizing about breeding grounds for specific genetic neural traits. :)