Things could have been so much worse. Last summer, Stephen Sondheim was reported as suggesting that Walt Disney was set to bowdlerise his immaculate deconstruction of fairytale mythos.

The great man rapidly refuted the story and, though the stage version has been trimmed, Rob Marshall's Into the Woods does indeed retain much of the original's bite and cynicism. It is still a film about the impossibility of happy endings. Some of it is very well sung. Most of it is well acted.

But, as we might expect from the director of Chicago and Nine, this version never quite takes flight. Fatally stranded between stage and screen, it seems uncomfortable in its own skin. What are you, Into the Woods? What brings you here aside from a desire to satisfy Disney's insatiable need for princesses?

The stage show’s rug-pulling two-act structure – devised in the first years of the Aids epidemic, when happy endings were rare – is undermined by the inevitable lack of an interval. A busy host of familiar fairy stories wind themselves about a baker (James Corden) and his wife (Emily Blunt), desperate to have children.

The witch next door (Meryl Streep) sets them a series of tasks that brings them into contact with Little Red Riding Hood (Lilla Crawford), Cinderella (Anna Kendrick), Rapunzel (MacKenzie Mauzy) and others from Angela Carter’s magical cabinet of sexual sublimation. When, after many adventures, all seems tidied away safely, greater, less easily solvable crises emerge from the woods.

The film's greatest problem can be addressed through an analysis of Streep's unfortunate hag. Marshall can't decide whether he's imposing pseudo-reality on the story or heightening its theatricality. By shooting on location – a largely awful take on the comic Agony takes place pointlessly in a waterfall – he inclines towards the former strategy.

Yet, for the first two-thirds of the film, poor Meryl labours under the sort of make-up that June Rodgers wears while singing Let It Go at the Red Cow Inn. Streep's enormous turn might have worked on the Great White Way, but it is positively absurd on screen.

Chris Pine stretches the limits of a very fragile voice as Cinderella’s Prince. Musical theatre veteran Kendrick battles with a change in her normal register. Corden bustles amusingly. The only remarkable thing about Johnny Depp’s dreadful turn as the Wolf is its determination to elevate Russell Brand’s various lascivious turns by comparison.

Thanks heavens for a terrific Emily Blunt who, as the occasionally tortured Baker’s Wife, seems intent on single-handedly battering the piece back towards respectability.

Thanks heavens, also, for Sondheim's durable score. Sending the audience out to Children Will Listen, one of his very best songs, guarantees a degree of forgiveness for preceding longueurs. It will just about do.