While I liked Allegiant it was not without problems. The ending didn't bother me, nor did the lack of science knowledge. I liked that the plot took us outside of the city to what was further beyond, which was bleak and disturbing. 
 I had two major issues with Allegiant. I couldn't stand all the bickering and arguing between Tris and Four. We had enough of that in Insurgent and there was already so much going on in Allegiant that it detracted from everything else that was going on. 
 Over the last couple of years I have come to love dual narrated books, but it didn't work at all in Allegiant. Their voices weren't distinct and I couldn't always tell who was narrating. A fact that was made worse because it didn't always alternate with each chapter. There were a couple of times that I got pulled out of the story a bit when I realized I had the wrong narrator.