I entered the plush Leicester Square auditorium for a screening of The Adventures of Tintin with low expectations and 3D glasses. Donning the latter and suppressing the former, I thought for a few pleasant minutes that my forbearance might be rewarded: the opening credit sequence, a zappy graphic medley in which cityscapes, crime scenes and villains morph into and out of one another, was excellent; and so was the first scene, which wittily showed Hergé himself (Tintin's creator, in case you didn't know) eking out a living by drawing caricatures in a flea-market, the array of his past clients featuring characters from all the Tintin books. From then on, though, it was downhill, and then some. Steven Spielberg's adaptation is not just a failure; it is an assault on a great body of art so thuggishly moronic as to make one genuinely depressed.

Make no mistake: the Tintin albums are great art. We could argue until the cows come home about what type of art they represent (narrative? Visual? Sub-cinematic?), but their greatness brooks no querying. Their characters, from melancholic and explosive Captain Haddock to proud and fiery General Alcazar to the vain and affected opera diva Bianca Castafiore, rival any dreamt up by Flaubert or Dickens for sheer strength and depth of personality. Their recurrent themes and symbols – the downfall of noble houses, host-guest encounters gone drastically wrong, tombs and their secrets, water, forgery, the Sun (to name but a few) – are entirely classical, the same found in Aeschylus or Shakespeare or Faulkner. They are eminently political, depicting, first from a rightwing perspective, then, increasingly, a leftist one, a 20th century characterised, just like the present era, by conflict over Middle Eastern oil, the perpetually unsettled Balkans, galloping technological progress, profiteering multinationals and arms traders who have one foot in the president's office. Best of all, they yield to a casual reader of seven the same amount of joy and wonder as they do to the most diligent adult scholar.

Here's a telling anecdote: after the premiere of a previous, equally doomed attempt in 1960 to adapt the albums for cinema, Hergé asked a boy leaving the auditorium if he'd liked it. No, the boy replied. Why not, inquired the crestfallen author? "Because Captain Haddock didn't have the same voice as he does in the books," the boy explained. His apparently naive take was in fact incisive, since Tintin was always premised on a set of implicit borrowings and relocations from one medium to another. Hergé's earliest strip-cartoons were billed as "movies" on paper; creatively, he was as indebted to the films of Buster Keaton and Harold Lloyd as to the novels of Jules Verne or the illustrated poems of Benjamin Rabier (which, long forgotten now, featured a tuft-headed boy called Tintin-Lutin and his dog). Hergé's remarkable achievement with the Tintin series was to pluck all these elements from their original contexts and join them together, holding them in perfect equilibrium, in a new, hybrid format whose conventions (speech-bubbles joined with left-to-right action, for example) he established in the very act of assembly.

Here, though, everything that found its form so well in Hergé's remix loses it catastrophically in Spielberg's. The slapstick – oars swinging round and bumping on heads, feet tripping on cats, and so on – is gauche and anachronistic. The plot (Hergé, like his almost-exact contemporary Hitchcock, was an absolute master of this) is hole-ridden and ridiculous (for what it's worth, it involves a kind of cut-'n'-shut weld of the plots of The Secret of the Unicorn and The Crab with the Golden Claws). The action sequences are not grounded in any credible reality. This is important: like so many children, I spent hours staring, captivated, at the single frame from The Broken Ear that shows Tintin trying to fire his speeding car over a level crossing just before a hurtling locomotive cuts off his path. (Will he make it? Look at the angles of approach, the lines showing the relative speeds of his car and the train. Might he just? Great snakes: he's pulled it off!)

Spielberg, a fine film-maker in his prime, captured the same exhilaration in Raiders of the Lost Ark, as Harrison Ford, or his stuntman, clung to planes and straddled gaping voids. But here, CGI allows for anything: galleons fly through the air, pirates skip gaily from one burning vessel to another; a sidecar splits from its motorbike and crashes through a building which itself is being borne down a ravine by a cascading wall of water, while Snowy flies through windows clinging to a falcon's tail before landing back on the sidecar, that in turn rejoins the bike … or something; on and on and on. It's boring beyond belief. When all you're looking at is pixels being shunted around a screen by some nerd in post-production, none of it counts.

But worst of all is the violence perpetrated against the core impulses of Hergé's work. The deep and disturbing power of the Tintin books lies in the way that they immerse the reader in an inauthentic universe, a world whose veneers are constantly being peeled back to reveal inner emptiness. This begins right back in 1929 with the very first adventure, Tintin in the Land of the Soviets, in which the commie-bashing hero, noticing visiting English Marxists gushing over Soviet factories, sneaks behind the buildings (and, by extension, the belief system they underpin) to discover that they're wooden façades: the smoke is made by burning hay; the clangs by a single man banging a piece of metal. It continues, with increasing complexity, through the figure of Haddock, who is posited between the lines as the illegitimate descendant of Louis XIV (the Sun King): the latter's gift to Haddock's ancestor Sir Francis of a château, Marlinspike, adheres to a well-established 17th-century convention whereby monarchs bequeathed property in lieu of recognition to their bastard offspring (the house even has a dauphin crest, symbol of royal filiation, carved above its doorway). The name "Haddock" means (in its French form, aiglefin) "phoney", "counterfeiter" – and, anyway, it's not his real one.

Neither, it transpires, is the author's. Not only is "Hergé" a nom-de-plume, but the same story of false identity and illegitimate royal descent turns out to haunt his family, too: his grandmother, a maid in a château, was impregnated by a visitor she never named but gave to understand may well have been the Belgian king (who was indeed a frequent guest at the château). Hurriedly "white-married" to the house's gardener, she gave birth to twin boys (Hergé's father and uncle), who grew up to sport moustaches and wear bowler hats. The Tintin books replay this covert family history again and again, whether through moustached and bowler-hatted twin detectives, or though the aria from Gounod's Faust repeatedly performed by Bianca Castafiore, which tells – once more – of a lowly maid made pregnant by a noble cad. And as they do so, their casts are dragged more and more into the vertiginous and hollow backstage zone where names, personae and the world itself are robbed of their semantic value. By the final album, Tintin and the Alph-Art, Haddock is left contemplating a giant "H", repeating to himself the nihilist mantra "None of it means anything!"

But Spielberg casts aside all that inconvenient content. Not only does he follow the English translation's mistake of substituting Charles II for Louis XIV as Sir Francis Haddock's benefactor (forgivable in the translation, since when it first appeared no one had drawn out the adventures' glaring subtext, nor had Hergé's own family secret been made public; unforgivable now that both have been discussed for two decades); he also slaps on, by the trowel-load, all this earnest rhetoric of authenticity. "Only a true Haddock can understand", "Be true to yourself", "Listen to your inner truth": lines such as these are repeated manically, as though we have wandered into a self-empowerment seminar – a seminar on monetisation through self-empowerment, to be precise.

In the books, money both stands for genealogical fakeness and is fake itself (a brilliant scene in The Crab with the Golden Claws shows Thompson and Thomson tricked into passing off the very counterfeit coins they've been charged with tracking down: a doubling of illegitimate faces and false "metal"); in the film it literally pours down, in one scene, from the skies, Haddock's reward for being "true to himself". Thus Hollywood's idiotic "message" is forced on an oeuvre that is great precisely because it drives in exactly the opposite direction. It's like making a biopic of Nietzsche that depicts him as a born-again Christian, or of Gandhi as a trigger-happy Rambo blasting his way through the Raj.

Perhaps this movie will be studied, in years to come, as a Žižekian example of a dominant ideology's capacity to recuperate its own negation, or something along those lines. For now, we just have to wonder how Spielberg went so wrong, or if he was in fact involved at all: so badly put together is this film that it's easier, and perhaps more comforting, to imagine a semi-simian marketing committee writing and producing it under the banner of his name. If your children love the Tintin books – or, more to the point, if they have an ounce of intelligence or imagination in their bodies – don't take them to see this truly execrable offering.