This book is so bad, I would discourage anyone from even starting the series. It's so bad, I wish I could recover the hours I've lost reading it. It's so terrible, that it completely annihilated any desire for me to ever read anything written by Veronica Roth ever again.
Let's get down to it. Remember there are spoilers ahead!
Regarding the story...
Before reading Allegiant, I'd read "The Hitchhiker's Guide to the Galaxy" and the point of that book is that it's downright ridiculous but in a smart manner. Allegiant is just plain ridiculous without having a reason to be. There are plot holes that are so big, they're black holes and they'll just drag anything remotely sane into them. I mean, the story itself, from Book 1 is farfetched. We're talking about a dystopian society where people are divided into 5 factions according to the personality trait that defines them. I mean, come on. It IS ridiculous, but you can put that aside and actually read the story because it's entertaining. In "Allegiant" you finally get an answer as to why society has been divided like it has and it turns that Chicago is an experiment where the "people outside" are trying to "correct" the genes from the population. If you're going "wtf" or "eh" right now, that's exactly how I felt.
Bottomline: the people of Chicago have been an experiment for about 8 generations. No one has ventured "outside" the fence because... why hasn't anyone done it? At the end of Book 2 it's revealed that they were all put there and that's what gives Tris and the others motivation to leave, but why hasn't anyone even attempted to do so before? There was no indication that they've been told not to leave the city or... anything. It's just ridiculous.
So then, these people are experiments. Right. The "Genetically Pure" people outside are trying to correct the genes God knows how, 'cause even after I was done with the book I was still wondering what the hell I was reading. I couldn't care less about Genetically Pure or Genetically Damaged or about the "Purity Wars" that apparently led people to create the experiments in the first place. There was a whole new twist to the story, but it was badly executed, and I didn't give a damn about any of it. I'm not even getting into the science of the whole thing.
Genetically Pure? Genetically Damaged? REALLY? REALLY? Oh God. You mean mutations? What? WHAT?
It doesn't make sense.
And if the plot is not enough to discourage you, let' move on to the characters.
Beatrice (Tris): Pretty cool character. Survives Divergent and Insurgent only to get herself shot and killed in Allegiant. Yes, Tris dies. And it's not even a death that makes sense or does her justice. This was a good character, strong and developed and she got pathetically killed. I mean, even Hedwig in Harry Potter got more attention than Tris in her death scene. It's okay if you kill your main character, but at least make it epic. At least make me feel like she died for something. All I felt was anger.
And I just got angrier as the book drew to an end.
Four/Tobias: This character is a lesson on how to ruin a good male lead. Make him awesome in Insurgent and Divergent and then make him whiny and pathetic in Allegiant. Seriously, Tobias is the best exemplification of what would happened if men suffered from PMS. I HATED him. Legit, HATED him in Allegiant. I don't think I've disliked a character so much since Edward stepped into the sun in Twilight and sparkled (shine bright like a Diamond, Edward). Tobias went from +1000 in awesomeness to -100 'go to a corner and just disappear' (he could use one of those black-plot holes for that).
There was nothing I liked about this book. I kept reading it just because I wanted to finish and write this review. I disliked the ending as it seemed rushed and I could not give a damn about the Epilogue and how they scattered Tris' ashes. She wasn't even honored for what she did. Her sacrifice was for nothing. There is nothing beautiful about this ending. It's insulting to the reader.
I am pissed with this book and I will just forget that it exists. I think you should too.