The unusually prompt follow-up to his chilling 2018 debut Hereditary, it's superficially the opposite of its predecessor: a film of exteriors rather than interiors, sunny rather than sombre.

For good or ill, Midsommar invites comparison with another of last years big-ticket horror items, Luca Guadagnino's remake of Dario Argentos Suspiria.

Yet it's also the same film in a different disguise, a parcel unwrapped one layer at a time until we reach a truth that stares back at us like a grinning skull.

There has been a lot of talk over the past few years about something called "folk horror" - that is, films about the survival of pagan cults in western Europe. The appeal is obvious, at least where white audiences are concerned: it allows the thrill of fantasising about savage, uncivilised practices with none of the guilt of attributing this to a racial Other.

Midsommar toys with the commonplaces of this subgenre, but in an uncommonly knowing way. The setting is a commune in rural Sweden, where the heroine Dani (Florence Pugh) heads for a summer holiday, tagging along with her boyfriend Christian (Jack Reynor), who's a graduate in anthropology, and some of his mates.

The Harga, as the commune is known, seems initially like heaven on earth (in a typically witty touch, one of Christian's fellow students is played by William Jackson Harper, best-known as a regular on the posthumous fantasy sitcom The Good Place). Clad in all-white garb, the members initially seem welcoming to a fault. But we might think we can guess where the story is going, particularly when phrases like "May queen" casually turn up in conversation.

Horror is conventionally about what is hidden in the shadows, but Aster inverts our expectations on more than one level. In Sweden at midsummer, daylight is constant - and though certain aspects of the story are not unveiled until the climax, we can see in retrospect that much was out in the open from the start.

Even before embarking on the trip, Dani has in a sense already faced the worst and come out the other side: this is a rare case where it's necessary to avoid spoilers for the beginning of a film, rather than the end.

For good or ill, Midsommar invites comparison with another of last year's big-ticket horror items, Luca Guadagnino's remake of Dario Argento's Suspiria. But Aster is less pretentious than Guadagnino, aiming to be genuinely distressing rather than fashionably "transgressive". He's also a more interesting stylist: his elaborately choreographed long takes, with groups of actors set at a distance from the camera, are grounded in the visual syntax of classic Hollywood, and are attractive simply because so few filmmakers today are attempting anything of the kind. At the same time, much about his technique feels ultra-modern: the pristine digital clarity of the images, the focal shifts that move us in and out of different subjective viewpoints, the psychedelic effects where the landscape ripples and billows like a sheet hung up in the wind.

Even more than Hereditary, Midsommar lives on the edge where horror meets absurdity, prompting the kind of laughter that comes from not knowing how else to respond. To a degree, it's a plus that Aster is working close enough to his unconscious that he hasn't entirely thought through all the possible meanings.

Is this, in some fashion, a movie about whiteness? Is there an environmentalist subtext? What do we make of the gender politics of the Harga (men and women have separate roles, yet equal status) in light of the veiled yet insistent sexism of Christian and his friends? Aster has described the film as a pervert's Wizard of Oz - meaning, presumably, a fairy-tale about an innocent transported to a foreign land where her magically ordained future awaits. This description too could apply to Suspiria, suggesting there may be something personal at stake for both filmmakers - as if both were fantasising, consciously or not, about just what sacrifices it might take to conquer Hollywood.