The billboards outside the cinema were patronising, noting how this "sacred", "high art" opera was finally being made accessible to all.

Forgive me, but Mozart's work was designed to be fun and accessible to all, composed for a working class theatre and using the 'low' Singspiel form.

"The Magic Flute" contains obvious elements of spirituality, symbolism and allegory, and its adherence to the principles of masonry (through the use of the number three, or masonic five-note figures representing women) is fascinating to explore. But the work is, most importantly, a pantomime, albeit a highly unusual, brilliant and exalted one. The Chamber Orchestra of Europe play the score faultessly, with touches both of Claudio Abbado's lightness and of Karl Böhm's weighty grandeur.

Branagh sets the drama on the battlegrounds of World War One. It's an odd choice, perhaps, but, for me, it is a choice that's both brilliantly considered and effortlessly sustained. During the overture, a long, imposingly sweeping shot introduces one to the environment (a surreal green pasture, soon to become a battlefield), sets in motion the drama's unravelling thread (we watch as a battalion of troops rush from their trenches into bloody conflict) and draws the eye to a statuesque, handsome young soldier. This is, of course, Tamino (glowingly sung by Joseph Kaiser), who we soon follow into the trenches, as he dodges gunfire and finally topples into a pool of murky water. "Oh help me! God help me!" he cries, as an ominous cloud of tear gas bears down upon him. This is visually exciting, dramatically absorbing cinema, and also cinema of the highest economy: not one shot or camera angle is misplaced; nothing can break the magic of Branagh's colourful and mesmerising visual aesthetic.

Some may accuse Branagh's interpretation of being banal - perhaps the same people who dislike David McVicar's "Giulio Cesare" for its unashamed frivolity - but I can't remember the last time I was so engrossed by Mozart's opera. The pacy, occasionally deliberately hyperactive camerawork is not tiresome but exhilarating; the CGI effects struck me as finding exactly the right balance between realism and surrealism. The Queen of the Night (sung with riveting hysteria by Lyubov Petrova) soars maniacally through the air in her Act Two aria, striking an imposing figure when silhouetted against the illuminated, spinning windmill wings behind her. Papageno (a reliable Benjamin Jay Davis), in his Act Two aria, imagines himself flying with bird-like ladies, finally diving into a floating pair of enormous lipsticked lips. It's rather ridiculous and also rather wonderful: even in this warlike environment, the opera's fantastical, fairytale genesis is never forgotten. Thus the interpretation is both traditional and fresh.

Branagh also removes the opera's overt references to masonry, preferring instead to concentrate on presenting a simple and direct tale of good versus bad. Yet the tale is nicely coloured. The Queen of the Night is no one dimensional bitch, but an unusually complex and sympathetic character: the sentiment of her Act One aria is believable and heartfelt; upon seeing Pamina's happiness in the opera's final scene, she tragically throws herself rather than falls to her death, Mozart's great accompanying chromatic conflagration highly poignant and the resolute final chorus tinged with sadness. And René Pape's resonantly sung Sarastro is, similarly, not a vacuous kingly moraliser but a sympathetic and troubled man, aware of the horror of war as he stands in a graveyard, dwarfed by rows of deliberately identical and faceless white tombstones, and determined to end the conflict, even if it means using innocent Tamino as a pawn.

But the film is not successful because it is insightful, but rather because it is so damned exciting. I realise that many will dislike it, perhaps for its rather Hollywood style, perhaps for its arguable reduction of a great opera to a Peter Jackson parade of CGI, but I spent the entire running time (the work is long, played with no interval, though most of the dialogue is cut) gripped by the unravelling tale and by the dramatically-loaded dialogue between Mozart's transcendental music and Branagh's vibrant visual style. Indeed, I was prepared to forget the film's flaws, however obvious and troubling they could sometimes be. I was not as concerned by the Pamina, Amy Carson, as some have been, finding her limpid vocal quality and easy delivery of the text compensation for some occasional struggle at the top. But the three ladies are problematic, apparently completely unable to clearly enunciate Stephen Fry's gloriously simple translation in their vital opening scena. The three boys are more easily understandable, but I disliked the increasingly saccharine smiles that Branagh bids them adopt, finding their apparent attempt at cuteness a profoundly false gesture: like the flute of the opera's title, they are elevated beings, neither good nor bad, and Branagh's characterisation here can only demean their important position in the work.

Yet such was the impact of the film upon me that I am willing to lay aside my concerns. I must warn that this must be watched at the cinema, and will not come across well on the small screen: imagine watching "Once Upon a Time in America" on a black and white television, or hearing "Das Rheingold" on a portable stereo. And I also suspect that I am in a great minority, having enjoyed the film, and critical opinion seems to sway strongly towards the negative. Yet at the cinema where I was last week, the small but pleasingly diverse audience was glued to the screen from first to last. As the overture played again over the closing credits, I shut my eyes and basked in this music of such extraordinary beauty, power and meaning, casting my mind back over the colourful, exciting and fantastical journey I had just taken, unable to speak. But also unable not to smile.