VIEWERS may be forgiven for approaching "Blue Ruin," a new thriller by Jeremy Saulnier, with a degree of caution. Moody, atmospheric, skillfully constructed and spiked with sporadic paroxysms of brutal violence, it's in many ways typical of movies by emerging filmmakers, most of which are designed to show off technical chops and little else. The last thing the world needs is another empty genre exercise.

Which makes "Blue Ruin" that much more of an exhilarating astonishment. Saulnier, whose first feature was the festival favorite "Murder Party," and who has made a name for himself in recent years as the cinematographer for Baltimore filmmaker Matthew Porterfield, certainly has chops to spare. From the first moments of "Blue Ruin," during which a man's hand emerges into the rising steam from a bathtub to warily turn off the spigot, it's clear that Saulnier possesses an uncommonly poetic visual sensibility, a gift for lyricism that pervades this tautly constructed slow-burn even at its most spurtingly graphic extremes. The story Saulnier tells is as simple and ancient as the Hatfields and the McCoys, but because of his taste for the off-kilter and an exceptionally confident hand, the audience never knows what's in store next on a journey that is both utterly familiar and unsettlingly strange.

That hand in "Blue Ruin's" first shot belongs to Dwight, a bearded loner who's living out of his car on a Delaware beach, scrounging cans and discarded food and breaking into empty vacation homes to clean up once in a while. Silent, brooding, opaque behind a pair of brown, mournful eyes, Dwight is almost immediately a sympathetic character - even more so when the source of his isolation becomes clear. That all-important pivot point sends Dwight - played by Macon Blair in an extraordinarily focused, expressive and nearly wordless performance - on a mission that, over a few days, changes his and several others' lives forever.

"Blue Ruin" might easily have been just another knock-off were it not for the rare transparency Saulnier and Blair bring to the enterprise, a willingness to subvert expectations of the genre they're working in even as they obey its most time-honored visceral conventions. Alternately methodical and amusingly bumbling, Dwight emerges as a reluctant example of the usual assassin/hit man/vigilante protagonist; during the film's most gruesome scenes, he's dressed in khakis and an oxford shirt, his face permanently contorted in an expression of pained disbelief.

Such sly upendings continue throughout "Blue Ruin," in which guns are plentiful but not bandied about aimlessly: They're tools, not weapons, and Saulnier makes sure that his characters have them conscientiously locked up. When things get bloody - and they do get bloody - the effect isn't Tarantino-esque as much as somber, grievous, clumsy and desperately, disquietingly messy. "That's what bullets do," one character says, bluntly, looking at a face that's been half-blown away. (Although "Blue Ruin" is a showcase for Blair's bravura performance, he's surrounded by terrific supporting players, including Devin Ratray and - hey, it's Jan Brady! - Eve Plumb.)

The most memorable set piece of "Blue Ruin" doesn't feature guns at all; instead it's an excruciating incident with a crossbow, which, to its credit, doesn't at all end up the way we've come to expect. Over and over again within the movie's economical hour-and-a-half running time, Saulnier brilliantly choreographs these surprises, either through astute writing or adroit, understated camera work. What's more, he infuses real emotion and humanity into a form that all too often treats characters like shooting-gallery rabbits, with the film's final gesture lending "Blue Ruin" a particular air of redemptive closure.

The world doesn't need another empty genre exercise. But as "Blue Ruin" reminds us, it can always use more filmmakers of Saulnier's resourcefulness, sensitivity and quiet assurance.