Allegiant (Divergent, #3) - Veronica Roth
Incredible.

ETA:
Was gonna leave it at that, but realized I'm a little too overcome with emotion to leave this review. When I'm returned to a more rational state will say more.

ETA (March 21, 2014): There are many problems with the book, as a fan I will admit that. Frustrating, and plot holes galore while reading.
I have been reflecting on this book for near on four months now (due to having to prod my friend along - ehem, Nell) and this has been the take away.

I came back to my review today and couldn't believe that the first word I thought of when finishing was incredible. But there you go, I did think it. Undoubtedly, it was the ending that had something to do with it, despite how much I despised it, it was indeed powerful.

I'd like to acknowledge very real complaints and positives shared by fellow reviewers. Here's a digest:
Mitchwho correctly points out
Here's the thing, Divergent as a series is built around one very simple, very obvious proposition: we should all be treated as individuals rather than stereotyped into some faction, Dauntless or Erudite or Candor (except Roth's doing the stereotyping anyway, like what's up with only the Erudite wearing glasses?)

Thumbs up for Christina's insight into the positives
For one thing, and this is pretty important, TRIS FINALLY ACTS LIKE SHE’S DIVERGENT. For the first two books, everyone keeps talking about how special Tris is because she’s Dauntless, Erudite and Abnegation, but, really, she acts like none of those things. The closest she gets is Dauntless, by the skewed definition of “does stupid, dangerous things for fun” rather than brave. In Allegiant, she displays intelligence, commits a selfless act, and shows bravery. This is the first time that I have seen signs of these things from her. When Four’s whining and moping about the fact that he’s not divergent and thus genetically damaged (seriously, dude, this is bullshit. staaaahp), Tris is totally logical and tells him to chill because he’s the same person he always was.