Fought with 19th-century tactics and 20th-century weapons, the hellscape of World War I was an almost sui generis abattoir, something Sam Mendes captures in the sometimes excellent, sometimes frustrating "1917."


The disgusting trenches, the dead horses next to piles of dead soldiers, the extreme contrast between idyllic fields one mile and literal scorched earth the next — Mendes samples it all.


And I do mean samples, as in tiny bits of different modes making a whole. At its weakest, "1917" really does feel like a video game, the protagonists compelled to move from one challenge to the next, in (mostly) real time.


We meet Lance Cpls. Schofield (George MacKay) and Blake (Dean-Charles Chapman) dozing in a field. For a moment, they are at peace.


It is April 1917 in northern France. Blake is awakened by a higher-up, told to choose a partner and report to Gen. Erinmore (Colin Firth). Naturally, he taps his pal Schofield., perhaps assuming the duty will be, in the context of open war, not that life-threatening.


This is incorrect, for Erinmore needs these two chaps to hand-deliver a change of plans to the Second Battalion commander, Col. Mackenzie: The attack on what the colonel assumes are retreating German forces is, in fact, a trap. German forces have not retreated and are instead massed in a way that will likely result in the slaughter of 1,600 British troops, Blake’s brother among them.


What immediately distinguishes "1917" is how Mendes, cinematographer Roger Deakins and editor Lee Smith present this story. It looks and feels like one continuous take (it is not, but they fake it pretty well), one tracking shot that follows our heroes into the landscape that inspired Tolkien’s Mordor (something that Peter Jackson’s Middle Earth movies have made it impossible not to think about here).


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This also means the story takes place in (with one exception) real time, which does something striking to the narrative. While contemporary warfare often takes place from vast distances (drones, missiles, bombs from above), "1917" reminds you that during WWI, it could be a mere 20-minute walk between safety and annihilation.


It’s a walk Blake and Schofield have to take through No Man’s Land, across enemy lines, past booby traps and barbed wire.


For a movie that is inherently kinetic (the protagonists must keep moving), it’s also quite intimate. We learn quickly that Blake is a good-natured chatterbox, quick with a funny story but no less focused in his mission than Schofield, his taller, more dour friend and companion. While Blake is excellent, MacKay delivers a tour de force as Schofield, a young man who has seen more violence and horror than anyone should encounter in a lifetime.


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A few well-known character actors pop in here and there for surgical-strike cameos, the most resonant of which is Andrew Scott ("Fleabag") as a seen-it-all officer who really wants his flare gun back, and Mark Strong as a commander who exudes professionalism.


But the vast majority of our time is spent with Blake, who loves discussing his family’s cherry trees, and Schofield, whose regard for the war is such that he doesn’t remember where he put his medal for the Battle of the Somme.


There are grace notes that also serve as plot points between the horror. Schofield and Blake must decide whether to aid a downed German pilot one moment, while a baby and de facto caretaker are found in a ruined Écoust village the next.


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Which returns us to the film’s central strength and weakness. One "continuous" shot suggests (or demands, rather) that the audience and characters are operating in real time (save for a plot device moment of blackout). This makes the scene changes seem like an increasingly improbable series of events, or at least makes them quite jarring for the viewer.


As our heroes become more exhausted, the vibe becomes more surreal, culminating in a tableau of fire that suggests (a tad on-the-nose, perhaps) that this is literal, post-death Hell.


It seems like "1917" wants to have it both ways, the you-are-there aspect of the mission coupled with moments that feel somewhat impossible.


Maybe this is a feature, not a bug. Perhaps because the audience is a full century removed from the proceedings, we know the lie in the idea that this will be the War to End All Wars. Both a snapshot and a meditation, "1917" is a well-executed glimpse of humanity’s ultimate futility.