Spoilers from the book if you haven't read it, and I guess the movie a well?
First thoughts: I really enjoyed this adaptation of one of my favorite books to this day! It was the best adaptation I could have thought of.
I don't have much to say about this movie, mostly because it kind of speaks for itself and there are a lot of fan backing it. In fact, they've already slated the second movie for production. Unlike Vampire Academy, I don't feel like I need to justify why people should go see this movie. Again, it speaks for itself.
I think the only problem I really had with this one is that there wasn't enough character development with the other characters besides Tris and Four. The acting was great, and I think they really captured the relationship between Four and Marcus as well as Tris' relationships with her parents after leaving Abnegation, but I didn't feel invested in Christina or Will, especially when Tris had to kill Will, I didn't feel it like I did in the book. I think this is mostly because, while the characters were named, their stories weren't really delved into.
The acting was brilliant! I felt no awkwardness at any time from any of the actors, and the choice they made in actors was superb. I was very happy with Shailene Woodley as Tris (even though I was pretty mad about the choice at first because I'd only seen her in Secret Life of an American Teenager, and she was a total over-actor in that show), but she really captured the bravery and unsurety of Tris. Theo James as Four was an interesting choice. I didn't necessarily see him as Four, but I think the deep voice helped and his true age did make him seem older like he did to Tris. But these two had great chemistry with each other, as well as great chemistry with the other amazing cast members!
I was happiest to see that they stayed very close to the book. I wish they had shown the whole Peter's eye thing because he deserved it. Also, when they go up to do the zipline, one of the Dauntless was Veronica Roth! I knew she would be there but not what scene, and I was so proud of myself when I saw her.
Overall, a must-see for anyone who read Divergent and those who enjoy action-packed dystopians! Also, I've heard that the sequel is already slated to be filmed, so yay! I mean, I didn't really enjoy the second one nearly as much as the first one, and the last one has way too many feels that I'm already dreading watching it in the movie theater, but it's worth it to start the journey of this series.