Some of the finest horror films use their platform to explore the impact of grief. The likes of Don't Look Now, The Descent and The Babadook are all, to varying degrees, defined by the effect loss has on a central character. And to that rank we add Hereditary, an indie horror that arrives in cinemas with a wealth of hype.

The film opens on the death of Ellen, mother to artist Annie. A complicated relationship and a painful familial history gives way to a building sense for Annie that something bad is going on, that events are turning sinister. Soon things escalate and turn supernatural.

Hereditary comes close to brilliance. For at least the first hour the film sustains a sombre tone and sweltering tension that prickles away at its audience. This first half is punctuated by two extraordinary moments that will surely be amongst the standouts of the year. One of these benefits from the talents of Toni Collette, whose frankly extraordinary performance manages to ground a film that becomes increasingly silly as it propels to an ending that doesn't feel fully earned. Collette is the kind of casting coup that a film like this needs. The rest of the ensemble support her well, with newcomer Milly Shapiro having a big impact as Annie's strange daughter. Gabriel Byrne gives good hangdog, and Alex Wolff finds a compelling way to present a testing character.

For all the frustrating elements of the film's narrative, what can't be denied is the talent on display. Debut director Ari Aster shows himself to be one to watch, skillfully directing the weightier moments that give Hereditary its punch. He is aided by Colin Stetson's haunting score and Pawel Pogorzelski's cinematography, which give the film a compelling beauty. And it all comes together with the kind of editing that jars the film, giving it a nightmarish quality (the skills of Lucian Johnston and Jennifer Lame). I can't fault the film for the level of technical competence on display.

It is tough to review a film that is sometimes mad, fitfully brilliant and, in its second half, really quite maddening without ruining the cinematic experience. To give too much away would ruin what fun there is to be had with Hereditary, a film that will surprise you. But as skilful as it is, with the kind of performance from Collette that lingers long after the climax, it can't match the hype, can't quite sit alongside recent horror classics such as The Witch, The Babadook and It Follows.

A Mike Leigh film crossed with Rosemary’s Baby andThe Wicker Man. That’s Hereditary, the directorial debut of writer-helmer Ari Aster. Two thirds an edgy family drama, one third a supernatural mystery, it’s not quite a horror film. But at just over two hours, it’s certainly forty minutes too long.

Annie (Toni Collette) is grieving the recent death of her mother. From Annie’s obsessive creation of dolls house miniatures featuring snapshots of their relationship, it’s clear that the mother-daughter bond was not a happy one. Wretchedly unburdening herself to a bereavement group, Annie meets Joan, herself bereaved and seeking solace in spiritualism. But Annie’s young daughter is exhibiting odd behaviours e.g. scissoring the head off a dead pigeon; Peter, her son, does weed in defiance of his mother. And her husband Steve (Gabriel Byrne) supports her with strength and sympathy, quietly simmering to the boil. But supernatural evils have been awakened – and can’t be stopped.

Philip Larkin would’ve loved this, a cinematic peer to his poem: 'They f*** you up, your mum and dad… Don’t have any kids yourself'. It certainly sums up Hereditary, in which the foibles of family life are the seed-bed of sinister forces. The camera closes in on a dolls house until only one of its rooms is framed – and a person walks in. And so the film begins. It’s a superb and unsettling suggestion that we’re at the mercy of forces outside ourselves, which will find us, even in our homes.

A slow-burn film, then, but with much to enjoy if you’re up for a long haul, notably Toni Collette’s fabulous performance as Annie. Awards seasons ignore such films but Collette credibly nails every nuance of motherhood, madness, fear and anger. You believe everything that’s happening, thanks to her and to Gabriel Byrne’s wonderfully underplayed husband. Aster creatively take his time building sustained threat: a fatal occurrence is made the more harrowing by focusing on the eyes of a character reacting to it over several minutes - only then revealing the aftermath. An assured change from jump-cut, jolty movies where the scares are cheaply forced.

It’s a motif that recurs – the ick and creepiness are almost subliminally seen, and only after we’ve felt them first through Aster’s cast. And yet horror aficionados will probably be disappointed – there’s little new here. The Babadook and The Others both dealt with grief and possession, The Exorcist gave us the creeps with characters squatting like spiders in the corner of the ceiling. And The Wicker Man left us stone-cold chilled with its ending. Alas, the chilliest thing about Hereditary is likely to be the air conditioning in the cinema.

A simple concept - as the title suggests - of the supernatural being passed down through generations, takes too long. Almost plotless, Hereditary has the running time of The Shining and Rosemary’s Baby. But it brings no kind of step change, as they did, and for all the hype it won’t be remembered in years to come. The Wicker Man (1973) achieved a more sinister and lasting effect in 88 minutes. There’s a lesson there.

Yet if you come it as a well-realised drama of raw intensity and are prepared for the subtle use of the supernatural on the side, Hereditary is a rewarding film. And in its own hybrid way, almost a unique one.