I liked the movie.
You have to understand what this movie was about..and what it was NOT about.
It was NOT about the evacuation at Dunkirk. It was not a documentary. It was NOT about the tremendous threat to the Army, the tremendous problems in getting 300,000+ off the beach (when they expected to get only 30,000). It was NOT about the several thousand who stayed back to hold off the Germans while most got off the beach. It was NOT about the Little Boats.
This movie was about 3 small groups of people; the problems presented to them by the Dunkirk events; and how they dealt with them - the decisions they made.
It was about a few guys on the beach; it was about a few (3) civilians in a small boat going to Dunkirk to help remove soldiers from the beach, and it was about 2.5 RAF pilots (we didn't see Michael Caine

)
Dunkirk was merely the pretext for putting these 3 sets of people in extremely difficult situations and telling how they dealt with it. And the writing was done such that the three groups converged at one point , and then diverged again at the very end.
Yes there were flaws. Yes it took a little getting used to the 3 timelines of 3 vastly different lengths.
The movie was a character study of 3 groups of people in a tight situation.
I liked it. I liked Tom Hardy's RAF pilot and the acting he did to portray the decision he chose.
If you were going to the movie to see a colossal extravaganza about Dunkirk - you will be disappointed because that's not what the movie was about. Dunkirk was almost a MacGuffin.