CANNES - Let's hear it for Xavier Dolan: not many auteurs have built up such a body of work by the age of 25 that the first and least arguable adjective that can be applied to his latest is "characteristic." The Québécois multi-hyphenate does not appear on screen in "Mommy," a restless interior epic of unconditional love between mother and son, but his presence in it could hardly be stronger or more idiosyncratic. Dolan's passions, neuroses and eccentricities fill every frame of "Mommy" -- even the frames themselves have his name written all over them, given the director's unorthodox decision to shoot 90% of the film in a distinctive, disorienting 1:1 ratio. "I'm still big, it's the pictures that got small," protested Norma Desmond in "Sunset Boulevard"; think of Dolan's aesthetic here as a uniquely literal interpretation of that boast.

Dolan has been labelled a cinematic narcissist in the past -- an accusation he has not always taken on the chin --  but that needn't be a bad thing. You could hand the same tag to any number of great artists who pour their personal vanities and insecurities into their work, from Woody Allen to Cindy Sherman; what's important is what their reflections simultaneously reveal of the audience. Dolan's work thrives on his own self-interest; it's the discipline and intensity of his portraiture that varies. Last year, he made his best film to date in "Tom at the Farm," a lean, razor-cut noir of queer desire and denial that seemed less personal at first glance (it was his first film adapted from another writer's material), only to articulate his sexuality in nervy, exciting ways.

With "Mommy," he reverts to the florid excess of 2012's three-hour transgender relationship study "Laurence Anyways," piling on the delirious stylistic affectations in this 140-minute three-hander to dazzling but exhausting effect: the precious aspect-ratio shifts, the saturated filters, the emotive oceans of pop music, the whirling dervishes of autumn foliage streaking the screen. If Dolan's last film suggested he'd got these mannerisms out of his system, his new one counters that the mannerisms are his system: If "Mommy" counts as a slight creative step back, and I would argue that it is, it's at least an elegant and purposeful one. (A sashay back, let's say, with the swagger of an artist who has proven this isn't his only option.)

Of course, a certain degree of too-muchness is required to articulate the loving, toxically too-much relationship between Diana "Die" Despres (Anne Dorval, star of Dolan's debut "I Killed My Mother") -- a feisty, tattooed widow staunchly resisting the expectations of middle age -- and her teenage son Steve (Antoine Olivier Pilon), a ADHD-afflicted problem child already building his juvenile-offender cred. From their first scene together, it's clear that the young terror is every inch his difficult mother's son, which is why they're such a devotedly dysfunctional pair -- aggravating each other's most aggressive impulses to shrieky, occasionally violent effect. Die's decision to home-school Steve seems a disaster waiting to happen, but after he adds arson to his strike sheet, who else will have him?

Dolan begins his film, somewhat archly, with a wordy series of contextualizing title cards that situate the narrative in the (very) near future, and detail a hypothetical government ruling that permits overwhelmed parents to bypass the courts and have their challenging children committed without passing Go. It's a needlessly complicated introduction that makes the film to come sound somewhat like science fiction; Die and Steve's household, however, is believably exceptional enough to render the mitigating circumstances unnecessary.

Their sparring is engrossingly abrasive, but the film risks wearing itself (not to mention its audience) out within a mere quarter-hour. Dorval and Pilon, both remarkable, are cranked up to 11 from the get-go, while Dolan's chosen aspect ratio forces cinematographer Andre Turpin into a claustrophobically repetitive routine of alternating, invasive close-ups. It's bravura filmmaking, all right, but the center cannot hold. 

Effectively opening a window in this expertly airless arrangement is another of Dolan's muses, the wonderful Suzanne Clement -- who so vividly played something of a Die type herself in "Anyways." Here, she's Kyla, a shy, stammering neighbour who takes an interest in the struggling widow and her careening son, and swiftly becomes a stabilizing third wheel in this lopsided family arrangement. (She's seemingly taken more with them than her own husband and children.) Steve takes a semi-sexual shine to her, too, while Die seizes her emotional support -- perhaps more hungrily than Kyla can handle.

Dolan finds an unsubtle but effective way to express the benevolent effect Kyla has on the family. 80 minutes into the film, the square image unfurls into soaring widescreen -- the cinematic equivalent of a lungful of oxygen, and a gesture that made the crammed Salle Debussy audience burst into spontaneous applause. It's a gimmick he repeats once more in the film, to decidedly more bittersweet effect, as Die dreams the regular life she and her son will never have.

"Mommy" is a film built on such grand aesthetic and emotional gestures, and some inevitably come off better than others. I love the full-scale sonic blanketing of Dido's wistful, unfashionable ballad "White Flag" over one establishing scene of mother-son conflict, but it's one example of heightened technique that Dolan repeats early and often. By the time we're swinging supermarket trolleys in empty lots to the unlikely strains of the Counting Crows' "Colorblind," we've entered a realm of designer pathos: it's lovely, but so strenuously meant to be lovely that I found myself resisting the effect. 

Dolan's indulgences aren't something to be grown out of, merely applied with more range and intuition as the years go by; in an art-house scene that currently defaults so heavily to the classically austere, his pop expressionism is as necessary as it is exciting. A kind of Xavier Dolan Lee Daniels film, fat with acting and shot in rich fluorescent beige, "Mommy" isn't his most sophisticated work -- but it's one that nevertheless demonstrates how much he's grown in the five years that separate it from "I Killed My Mother." There, Dolan played the petulant son of Dorval's harried mother figure, framing the film entirely from his own demanding perspective. In "Mommy," he tells much the same story, but cedes the role of the child to someone else, all the better to see both points of view. It's a film of generosity in chaos, maddening but alive, threatening to shatter its formal 1:1 imprisonment at any given moment.