Beasts of the Southern Wild, Benh Zeitlin, 93 mins (12A)

This Sundance-winning fantasy is a cajun-spiced primal stew of a film, until cutesiness creeps in

Quvenzhané Wallis and Dwight Henry in 'Beasts of the Southern Wild' (Cinereach)

The esteemed American critic A O Scott, recently reviewing the torridly dreadful Florida-set thriller The Paperboy, used a deliciously apt phrase – he called the film "a hot mess". That's equally applicable to a much better feature set in New Orleans – Beasts of the Southern Wild. The exuberant debut by 29-year-old Benh Zeitlin – top drama winner at this year's Sundance Festival – isn't just a hot mess, it's a cajun-spiced primal stew. Unquestionably bold and original, it's the strangest film we've seen this year – and I only wish I liked it more.

At once rooted in reality and dream, Beasts is a delirious attempt at Louisiana myth-making – indeed, at a sort of neo-prehistoric cinema. The time frame is, apparently, today, and the setting a water-bound territory called the Bathtub, where the poor population (mainly but not exclusively black) live in lean-to shacks and sail ramshackle boats made from old car bodies. The heroine and narrator is a small girl named Hushpuppy (Quvenzhané Wallis, aged six during the shoot). When I say "narrator", I don't just mean that she's telling a story, but that she's also narrating her worldview – describing and thereby creating the entire universe before our eyes.

Hushpuppy lives with her drunken, agitated father, Wink (Dwight Henry, in civilian life a baker), who mainly nourishes her on whole broiled chickens. Largely left to her own devices, Hushpuppy communes with the livestock (she has a gift for hearing the heartbeats of pigs and fowls), occasionally makes drastic attempts to feed herself (lighting the stove with a flamethrower) and ponders her memories of an absent mother. That lady's mere passing presence would make water spontaneously boil: she's never seen, but is represented as a voice and a comforting waft of 1920s jazz.

Life in the Bathtub seems to consist largely of boozy carousing, firework displays and impromptu seafood feasts, fountains of blood-red crayfish cascading across the screen; they must have had a jolly time making this film, and a smelly one too.

Then the rains come down – leaving us to interpret Beasts as a magical-realist representation of Hurricane Katrina and its effect on a community. Bathtub dwellers are evacuated to a care station, where unthinkably, Hushpuppy is put into a neat blue dress, her hair tied in ribbons. She promptly skips captivity before, in an odd narrative jump, she and other children end up out at sea, visiting the Elysian Fields Floating Catfish Shack – a maritime brothel where, amid more vintage jazz, the little girls find mother surrogates to dance with in a tender, highly coloured idyll.

The film's single strangest element is a marauding herd of apocalyptic beasts called aurochs. In reality, aurochs were cattle, but as summoned up by Hushpuppy's imagination and Zeitlin's effects department, they become a gigantic breed of tusked pot-bellied pig – rampaging Hogzillas. Together with repeated images of crumbling ice cliffs, the aurochs bring the film a bizarre apocalyptic flavour. With Hushpuppy destined to face off against these ferocious yet oddly winsome monsters, Beasts finally suggests a swampland version of Where the Wild Things Are – both the Maurice Sendak book and Spike Jonze's fanciful film adaptation, although Beasts has shades of tweeness that aren't in either.

Co-written by Zeitlin with Lucy Alibar, adapting her own play, Beasts is more generally the product of Court 13, a sort of community arts collective – which is what gives the film its peculiar immediacy. The overall visual energy suggests everyone weighing in for the sheer joy of it, rather than just a professionally executed project: look, for example, at the image of a wrecked house standing in deep water, planks shooting from its roof like spikes. Beasts doesn't entirely convince me either as coherent narrative (not that it matters so much) nor as a quasi-spontaneous imagining of a poetic universe. But as an installation art project on a huge scale, it's pretty much sui generis – an attempt to transform the world into a lawless adventure playground.

Still, some aspects of Beasts are frustratingly gauche, or twee. Quvenzhané Wallis is a bracingly uncute child, stomping around in white wellies with a solemn scowl that suggests she's neither playing nor acting, but just going about her business and the camera had better not get in her way. That she's facially rather inexpressive works to the film's advantage. Yet cutesiness still creeps in via the voiceover, which mixes earnest Malick-style mysticism ("I see that I'm a little piece of a big, big universe and that makes things right") with a knowing attempt to capture a child's artless sense of self ("In a million years, if kids go to school, they'll know that there was a Hushpuppy and she lived with her daddy in the Bathtub").

The boisterous score by Zeitlin and Dan Romer, a sort of Crescent City revision of Michael Nyman, is typical of the film's tendency to get carried away by its own high spirits. You know the deal: you don't have to be mad, or drunk, or waterlogged to live here, but it helps. Despite its community-project roots, the film still feels awkwardly like a fantasy about blackness and the authenticity of grassroots living (not that it's necessarily relevant, but Zeitlin is white, from New York and a graduate of Wesleyan). Beasts of the Southern Wild is a wonder but it's also an uncomfortable case of nostalgie de la boue, literally – a yearnin' for the bayou mud. It's a hot mess all right, and largely in a good way, but it may be more your bowl of gumbo than mine.

It's not all Passport to Pimlico … Dark Ealing is a season at London's BFI Southbank highlighting the more nocturnal side of the time-honoured British studio, with features such as 1947 thriller It Always Rains on Sunday. Liberal Arts is that rare beast: a romcom with brains, starring Elizabeth Olsen and director Josh Radnor.