Well, the series finishes like it started: Meh. This one picks up where the second one left off, with Tris and crew finding out more about Outside the Fence and the reason why their society is the way it is. The pacing is better in this one than in the second, so that's a plus.
--Interesting (if somewhat nonsensical) premise, that people are sorted by and live according to a single characteristic
--Postapocalyptic Chicago setting, with expansion beyond
--I still don't buy the "chemistry" between Tris and Four--I found myself skipping over all of the romantic situations
--Unrealistic story for that "universe." For example, I found it hard to believe that the government wouldn't come and put new personnel in place when it became obvious that the others' memories had been reset.
--Wandering verb tenses--it's mostly told in present tense, except where it slips and lapses into past tense (I'm an editor, and the ones I'm talking about are not for, say, flashbacks within the story; they're just mistakes.)
--The biggest thing I had a problem with was the narration at the end of the book. This is supposed to be Tris' story--where the hell is she? I couldn't care less what happens to Four.
This is a decent series to take to the beach, or read on an airplane. Just don't think too hard about it.