I LOVED the first two books in the Divergent series so much, and I was incredibly excited for the final novel to come out, however, I was left slightly disappointed. I feel the explanation behind the creation of Chicago was quite weak and dull, there was no real action or excitement, and it was quite a slow build up, and then the end was just depressing. I felt it was a little rushed and the writing was no where near as good as the first two, to be honest - please forgive me - it seemed a little Stephenie Meyer-ish. Sorry.
It wasn't terrible, but it just didn't live up to my expectations, and I'm not entirely sure that I'd recommend the series to you if you've not started reading it from the beginning yet, but if you've read the first 2 then you should probably read this, just because you'd probably go insane from curiosity if you didn't.