Just saw it last night. Thought it was fantastic.
It brilliantly captures the hellish intensity of war yet manages the difficult feat of doing so without the need to resort to arterial sprays of blood or severed limbs. Rather the impact is in its brutal audio and stark cinematography; be it the deafening scream of dive bombers, the thunderous crack of gunfire, or the near constant pulsing score which modulates with the action yet lurks in the background even in quieter moments, so that like the characters, we're reminded that the violence is only ever on hold, never truly absent.
The action, when it does come, hits like a freight train, and is designed to be frightening rather than thrilling. These guys aren't fighting for glory or even for victory; they're fighting for survival.
It also deserves props for never preaching; it has emotional moments, but they never feel cheap or tacky. There's little character development, but honestly I didn't feel this was a flaw; the film isn't about the personal lives of these guys, but rather how they respond to the extreme situations they're put through. Performances are strong across the board, with the big name actors wisely underplayed so as not to distract.
Where most war films try to capture the broader geopolitical context through the story of a squad or unit, Dunkirk goes for a more minimalist approach; it's less a story than an experience, less a journey of heroes than a raw portrayal of what it would have been like for the average guys caught up in the madness, and it pulls it off magnificently.
A 9/10 from me.