For the most part I really enjoyed it. It's everything you'd expect Christopher Nolan would do if he made a war film. I feel like his biggest inspiration in making this was The Thin Red Line. And while this does deal with a war, it's more of a survival movie and you do feel intense throughout it. Even though it's PG-13, there are times where the intensity feels like any rated R war film.
The highlight of the movie is easily the visuals and sound. The IMAX shots were incredible and it really helps creating the massive scope and scale this movie has. it's almost unlike anything we've seen before and Nolan and his team did a much better job on not constantly switching aspect ratios like they did with Interstellar. The sound and score was excellent, you feel every bullet that comes out of those planes.
The movie has three distinctive stories with 3 timelines that intermingle with each other (The Air, The Sea, and The Mole). One of which is arguably much more complex and interesting (The Sea). The cast did a great job, however you don't get a whole lot of character development which I think was needed. I wanted more story out of the characters whether it be before the evacuation started or during. The only exception would be whenever the movie deals with Mark Rylance and Cillian Murphy (aka the Sea).
The other problem I have with it is Nolan's artistic structure for the movie. It was like if someone had the control of a VCR and kept rewinding and fastforwarding like a Robot Chicken episode. A straightforward narrative would have been just fine, but that's just me. And also because of the loud sound design and music (and their cockney British accents), it was very hard for me to decipher some of the dialogue.
Overall, it's Nolan's most impressive visual spectacle to date even though it is lacking in character development. This is a movie you have to see in a real IMAX to get the full effect for.