In my experience, in order to enjoy movies based on books, you have to recognize that they are only based on books. It is not meant to mirror the book, just loosely follow the plotline. If you compare it too much to the book, there will be no room to enjoy the movie itself.
I recommend that you watch the previous movie, Divergent, before you see this one. This movie picks up where the other leaves off and continues the plot. You will be confused if you do not know anything about the story, but only at first. The movie does a good job catching people up.
I really liked how the actors portrayed their characters’ emotions. I particularly noticed that Shailene Woodley was incredible at portraying emotions. She can make a miniscule change to her face and change to a completely different emotion, making her an expert at her trade.
The movie had good balance of predicting what was going to happen and not understanding anything at all. There were plot twists that totally blew me away, as well as moments where I guessed what was going to happen, but it was more gratifying than boring.
When the movie ended, I was completely satisfied, and I was still affected by it well afterwards. The plot was a roller coaster that left me feeling excited and happy, and not only did it make me want to see the sequel, it made me want to show other people the movie.