This can be brief: Dunkirk is one of the best movies I have seen.
I was rather dragged-along to the cinema by my wife, who is currently reading the history of World War II; but from a couple of minutes into the movie I was gripped, held, and never let go until the end. It is extremely exciting, deeply moving, indeed inspiring.
(And - related - there is no trace whatsover of political correctness - what a blessed relief that was!)
The movie seems very original in many ways: it is done as a classical epic, when we are thrown into the middle of action without set-up or explanation. It has little (but telling) dialogue. There is no padding - every scene tells. It relies on excellent acting rather than stars.
That said, it was almost unbearably affecting at times - both positively as well as negatively. Indeed, the moment when I came nearest to losing control, and had to gulp-back an actual sob - not entirely effectively, was actually the happiest scene. But it would be hard to watch the movie again, knowing the effect it will have.
Anyway, I hope have said enough that you can make up your own mind about whether this is the kind of thing you want to experience.