In response to some of the criticisms of the film, I'll offer these points to consider...
Much has been made about the film dialog being "hard to hear." This seems most evident in the RAF story line. I believe this is actually intentional. Hardy, I've read, has a total of 10 lines in the movie even though his plot line comprises about a 1/3 of the film. Almost all of his communications to us in the film is non-verbal. The storytelling Hardy does with just his eyes and eyebrows is amazing. We get the gist of what is said in muffled communication on his radio, but we don't need to hear every word uttered.
Regarding the lack of character development, the problem with becoming invested in central characters in war movies is we then begin to care more about them than their comrades in arms. Think of the "red shirt guy" analogy from Star Trek. The deaths of "extras" aren't as traumatic as long as the protagonists of the film keep going. It's said that Nolan's approach was to have us view the British Expeditionary Forces as a sort of "living thing" as a character instead of just getting us to care mostly for a few of the 400K trapped souls.
I thought the film was an amazing work of storytelling that didn't fall into the trap of following war film formulas. I three of us in my family thought it was very gripping. The cinematography was jaw dropping often throughout.