This is not a love song: "Blue Valentine"

You can tell Blue Valentine is something different from the Hollywood norm - that there will be no last-reel reunions, no simple happy endings - from the manner in which a family dog gets it within the first fifteen minutes, knocked down by a car and dumped unceremoniously by the side of the road. The dog belongs to troubled couple Dean and Cindy, and its death is indicative of a wider sickness permeating this blue-collar Pennsylvanian household: as becomes increasingly apparent, the poor mutt must have been running away to find a more loving home for itself.

The early scenes of Derek Cianfrance's drama detail the first few hours after the dog's disappearance, and appear to set the principals' roles in cold, hard stone. While the harassed Cindy (Michelle Williams) cooks and cleans and readies the couple's young daughter for school, Dean (Ryan Gosling) bums around the place in terrible leisurewear, his hairline receding, his hands splattered with paint; he joins his wife in the shower later on in the movie, and this, combined with Gosling's usual scratchy presence, conspires to suggest this is the first time Dean's seen hot water in weeks.

From his sudden insistence "we have got to get out of this house", Dean evidently has a sense of the toxic psychic forces draining the pair of them, but his idea of an escape is merely to cash in a set of coupons he's been hoarding for a tacky motel nearby, dumping their kid on their parents. (Inevitably, Dean's first movement once the couple checks into the motel involves draping himself across the bed, while Cindy acquaints herself with the limited kitchen facilities.) Just as we're hunkering down for two hours of grim domestic discontent, however, Cianfrance and his co-writers Joey Curtis and Cami Delavigne pull the first of several surprises here.

The film flashes back to Dean and Cindy's younger days, so as to show how they got here, and where all their naive good intentions went. These flashbacks may as well feature two different actors. Gosling, as Dean the removals guy on his way up in the world, is cocky, charming, invincible ("I'm never going to get old"); nowhere is the seething rage that's never too far from the surface in the present-day scenes. Williams, as a student from a home in the painful process of breaking up, is smart, caring and sensitive, not the careworn individual we'll elsewhere see being routinely undervalued in her personal and professional lives.

Each sharp, measured cut back and forth between the two realities is like a slap in the face for conventional movie notions of romance; what we're witnessing here is the death of love, the narrative's sustaining mystery a whodunnit of the heart. In 2000's Stir of Echoes, the American cinema's last wholly convincing and uncondescending screen portrayal of a working marriage, Kevin Bacon and Kathryn Erbe played fully-grown outsiders given cause to regret the way their lives had turned out - they could have been Kurt and Courtney, if the music biz hadn't come calling and all their creative ambition had withered away to naught.

Dean and Cindy, in comparison, are kids who don't really have a clue what they've got themselves into - they could be K-Fed and Britney, if they'd settled in the sticks somewhere and tried to raise their offspring as best they could, a couple whose first response to every problem is to try for another kid, failing to realise it was this unthinking assumption of responsibility that got them into this mess in the first place. (Williams does an especially convincing impersonation of Britney in her tired-and-braless phase; it makes a funny kind of sense the actress should go from this to playing Marilyn Monroe.)

Above anything else, though, Dean and Cindy are everyday, flesh-and-blood people, all needs and desires, frustrations and regrets. Mere mortals, in other words: Cianfrance scrutinises them in tight close-ups, capturing flushed skin and furrowed brows, traces of mayonnaise left behind on an upper lip, the physical and emotional traumas playing out on the face of a young woman submitting to an abortion procedure. (The film is nothing if not a corrective to the multiplex cinema's recent blithe portrayal of unexpected pregnancy: we are very much in the room as Cindy slips her feet into the stirrups.)

Given how the American cinema has defaulted of late on providing honest romantic entertainments, there is obvious value in the bracing corrective Cianfrance provides: one way of approaching Blue Valentine is as a film that shows what might actually happen to all those characters played by Gerard Butler, Matthew McConaughey and actresses called Jennifer and Jessica once they've come to realise they have less in common than their contrived narratives suggested.

Yet I think it's possible to admire Cianfrance for having the courage of his convictions and still not be entirely on board with his essential project. The soundtrack ("You Always Hurt the One You Love", "Smoke Gets In Your Eyes") is a little too on-the-nose, as though the filmmaker were more interested in making an ironic trailer than what a contemporary couple might actually listen to. And some of the motel scenes drift into that knock-off Cassavetes naturalism that actors and directors love, but which generally proves a drab experience to sit through.

Certainly, there's a degree of torturousness and breast-beating that makes the film less of a knockout than it might have been: it basically takes two hours to do what Ten City's "That's the Way Love Is" does so soulfully and magnificently in somewhere between five and ten minutes, depending on the mix. (I wonder if only the editing keeps the film from lapsing into terminal monotony.) See it for the performers, and the scrupulous even-handedness of its set-up - in which it at least has the nod on something like Kramer vs. Kramer - but for heaven's sake don't see it with someone you love.

Blue Valentine opens in selected cinemas today.