It gives me no pleasure to say this, but War Horse is Steven Spielberg at his most mawkish and least convincing. This is a noble but misjudged failure that finds a master director seriously at odds with his source material.

For a film that strives so hard for emotional heft, it falls frequently, spectacularly short. Episodic, overlong and often just plain weird, this is a lachrymose concoction of 40s Hollywood studio picture, WWI epic and family drama.

In making a film based on such unusual material – a children’s book told from a horse’s perspective and the subsequent stage play that realises the story through puppetry –  Spielberg was always going to have to address a major issue: how to capture the right tone and translate this into a piece of cinema. The answer seems to have been to make a film stitched together from other, older WWI movies.

Peter Mullan and Emily Watson (spouting much clunky, expository dialogue) play the Narracotts – toiling farm folk, financially yoked to cruel landlord David Thewlis. When Mullan buys a nag that sinks them further into debt, it looks certain they will lose the family home. Step forward the couple’s son Albert – newcomer Jeremy Irvine – who puts ‘Joey’ to work on the land (cue first ‘rousing’ Spielberg moment), forming an unshakeable bond with the beast. When the plough fails, Joey is sold on to an army officer (Tom Hiddleston) for the imminent war effort.

The first twenty minutes of War Horse are, frankly, disastrous and hobble the film before it gets out of the starting blocks. This opening stretch is one of the oddest in the Spielberg canon – a cross between The Darling Buds of May and How Green Was My Valley that veers between earnest drama and comedy and never feels like a comfortable fit for this director. It’s evident what Spielberg is aiming for, but – despite typically strong cinematography from Janusz Kamiński – the film feels more like Ron (Howard) than John (Ford). Opinions will be divided on Irvine’s performance,  although it’s not his fault that he is required to constantly stare dreamily at Joey, in moments that suggest he should maybe get out of the stables for a bit and meet a nice local girl.

Things improve considerably when Joey is put into battle as part of a near-suicidal cavalry charge against the Germans. Spielberg gets the big guns out here, employing the full arsenal of forty years of cinema experience. The result is exciting, resonant and brutal. It is a tremendous sequence that stands alongside the best work of this brilliant, natural filmmaker. The introduction of actors like Hiddleston and Benedict Cumberbatch lend the film an air of quality Brit drama and there is a sense that War Horse might settle into thrilling, Sunday afternoon fare. But when Joey is captured by the Germans, the film starts to falter again.

The basic problem in War Horse is one of connection, particularly Speilberg’s to the material (is there really any? It never feels like it). The characters that interact with Joey feel like stock figures and broad caricatures, robbing the film of emotional power and interest. War Horse never feels like a journey – for either Albert, Joey or the audience. John Williams’ score is (over) employed to create a sense of the epic that the film never attains. And Richard Curtis’ script is a very odd beast indeed. You would’ve thought that the man who wrote one of the most spectacular and moving elegies to war ever (Blackadder Goes Forth) would nail this stuff, but the dialogue is unnatural and clunky throughout.

There are glimpses of a greatness that might’ve been. And a scene in no man’s land – involving a trapped Joey and the warring German and English armies is, in visual terms at least, magnificently realised. But at 146 minutes the film is too ragged and unfocused. It stumbles where it should be fleet of foot, and too often pulls up short when it should be taking us on an exciting ride.

A couple of weeks after seeing the film I ended up winning a copy of the Michael Morpurgo’s original novel in my local film quiz. A slim, economic fable with tight narrative focus, I can see why it has become such a powerful and enthralling read for children. I’ve never seen the stage show, but its success seems to rest on the remarkable use of a puppet horse which has wowed audiences worldwide. In Spielberg’s film, despite having a quality cast and a real horse at his disposal, the strings are all too visible to see.