This wasn't bad, but it was a bit of mismanaged expectations. Many will go in expecting a Historical War and action movie -- what they'll get is a vignette movie telling 3 different stories, with overlapping timelines. A British soldier pooping and fleeing from the pending german advance (over a week), a British guy with a boat coming to save them (over a day), and a RAF pilot (over an hour), and how those stories intersect. If it sounds overly complex, it is, but the stories individually aren't bad -- the same with the movie.
Reviewers liked it more than viewers with a 93/83 rating on rotten tomatoes. I was more with the viewers. It was a good 3 or 3.5 out of 5 star movie. Solid, well written, reasonably active, well filmed. But a little overly complex, and not completely memorable. It told a few stories well, and I felt like I got my value out of watching it, but it didn't move me in any way.
Snowflakes complained because movie didn't have many people of color or women, in a historical movie about a british defeat that had virtually no people of color or women involved. I think they wanted Django Unchained version of history.
That of course got the rational people to play "mock the historically illiterate".
But overall, it wasn't a bad movie. It just wasn't as good as many had lead me to believe in might be. Plus I saw Hacksaw Ridge (2016) on HBO the same weekend, which was a far better war movie, and movie in general. So Dunkirk was eclipsed by a better film.