I really hate when a book that you've been looking forward to fails to meet expectations. Case in point, Allegiant. It wasn't bad. It's just that it failed to impress anything other than being the last book in a trilogy. It wasn't any one point, like the ending heard round the world. Which, by the way, was the most unsurprising ending ever.(show spoiler)
To avoid turning this into a complete dissection of my issues with this book, I'll go with this. My biggest problem with the book was Four. I hated to see such an interesting character previously, brought so low personality wise. Seeing him supposedly as he was "pre-Tris" was a serious discredit to him as a character and the series as a whole. I get that it was there to show how Tris "made him a better person", but blah blah blah. I hated it.
Allegiant as a whole just seemed as a book put out to make the biggest splash. And that it did, just not in the right way. It lost the flair that made Divergent good. It even lost the semi-suspense of Insurgent, and that is saying something.