If the measure of a movie is the decibel of debate that follows the closing credits, then The Voices does its job.

The presence of a starry cast (Ryan Reynolds, Gemma Arterton, Anna Kendrick) is, like many aspects of this movie, a shiny veneer to confuse the viewers.

This is a movie that overstays its welcome then, like the gatecrasher who produces a keg, veers back to warm acclaim once more. Is it right? Is it wrong? Does it work? Is it justified, tasteful, funny, horrific? Yes and no, but not necessarily in that order.

No wonder the story - by Michael R Perry - hung around on Hollywood's fabled "black list", the toxic yet tantalising hot potato scripts that never get made and then eventually do.

The story has likeable - then not-so-much - bathtub worker and all-round oddball Jerry Hickfang (Reynolds) whose barbaric past and uncertain future, combined with a hefty drug regime for a mental health issue make him the most unreliable of unreliable protagonists.

He develops a crush on the "English chick in accounting" Fiona (Arterton) but dating matters go somewhat awry and he is left cleaning up the mess with a range of knives, saws and air-tight storage containers.

He is not helped by the voices in his head. Especially when they are not in his head. They come from his foul-mouthed Scottish cat Mr Whiskers and his lumpy, good-natured dog Bosco (both voiced by Reynolds). Good and evil, see?

A further cacophony of confusion comes from his fridge where his growing collection of heads have feisty opinions of their own.

The trickery - the fun? - in the story of a man not entirely in control of his reality comes with director Marjane Satrapi's teasing sets. On drugs, life is drab and colourless and the bloody reality of his sprees are presented in their Seven-ish, blubbery glory.

Off drugs, free from such dampening restraints, the world is pink and nifty and butterflies dance around Hickfang's head and he is both dumb and dumber in his spaced-out fogginess.

"Pretend everything is fine," says Mr Whiskers. "It's got you this far."

It's easy to see why action hero Reynolds went for this small-scale project which has yet to get a UK release. It harks back to his fun, hapless days of The Proposal and requires the kind of gymnastics of snarl and charm that stretches his actorly muscles constrained by a superhero one-piece.

He walks the tightrope well. Kendrick, meanwhile, is more assured than Arterton, who wobbles in her blowsy role (some accomplishment for a head).

Whether it is a black comedy, a horror film or an exploration of the origins of mental illness is what will keep the film in mind long after the closing credits (a jaunty song and dance number with Jesus driving a forklift) have faded to dark, dark black.