The script of "Dunkirk" makes a complex effort to weave together independent story lines in the course of one of the epic displays of military (and, at its most basic, human) effort in history. While there is much to appreciate about it, the script at large is undermined at least a bit by the dialogue. The dialogue tends to be spare -- almost to a fault. Due the variety of British accents and the high-intensity nature of the scenes, there are expository items that are too easy to miss for an American viewer who might be stumbling to perform an accent translation. The sparing quality of the dialogue also makes it possible for the viewer to miss clever connections embedded within the storyline.
To the credit of the actors, most of the acting is understated and serves to underscore the projection of a stiff upper lip that fits well with the story arc. Certain characters deserved more screen time (foremost among them, the pier-master played by Kenneth Branagh), and it becomes difficult at times to appreciate the individual actors' performances since the scenes have a way of making many of them look quite a bit alike -- especially when their faces are covered in oil.
The lighting and cinematography have a strong periodic effect, making everything seem gritty and metallic without being excessively harsh. The opening of the film introduces three different stories via the use of screen titles -- and, frankly, the film likely would benefit from a few more of them along the way in order to help the viewer see where these parallel tracks are heading. One quibble worth noting: The title introducing the evacuation experience from the pier uses the word "mole", which to an American viewer means that one of the characters involved is a double-agent. That turns out not to be the case, as the word "mole" refers to the pier itself. But the confusion could easily cause a complete misinterpretation of a big portion of the plot if the viewer is looking out for a character to become a turncoat.
The film is mercifully gentle with its use of special effects and is sparse with the blood and gore of an ordinary war movie. Many scenes take on a naturally epic scale that occasionally doesn't do complete justice to the truth. "Dunkirk" tells a necessary story -- it's a tale of honor and heroism, and though it shouldn't sit right next to classics like "Patton" or "The Right Stuff" or "Twelve O'Clock High", it probably merits a place on the shelf immediately below. It isn't a documentary, nor even all that close to it -- an entire movie could and should be made about the pier-master -- but it does poetic justice generally to the cause.
Bottom line: Occasionally confusing (by design), "Dunkirk" tells a necessary story of honor