I sneaked into the cinema very late at night, in a frowsy English provincial town, when nobody was looking. The last middle-class person in Britain to see the film Atonement. I had the theatre to myself, but still drifting about in the air were the mews and gasps of contentment from the thousand upon thousand who had got there before me, who had sat in their seats, enraptured by Keira Knightley’s minxy, petulant, aristo underbite while digging away at their Häagen-Dazs.

Atonement is set for Oscars, it is already being said, especially in America, where it doesn’t even open until December; for Keira, for the director, Joe Wright, maybe for cheeky James McAvoy, who managed to remain familiarly cheeky even while dying of septicaemia at Dunkirk. He would have done his agreeable cheeky stuff even in Schindler’s List.

“The British are coming!” Colin Welland proclaimed from the podium back in the early 1980s, after the critical success of another exquisitely crafted, resolutely middlebrow British film, Chariots of Fire. And, since then, British success at the Oscars has been greeted back home as a victory for decency, intelligence, compassion and honesty of performance, a plucky broadside against the hollow cartoon dross of Hollywood. All those famous novels rendered implausibly beautiful by Merchant Ivory, David Lean’s A Passage to India, Anthony Minghella’s The English Patient – films that, because they are based on respected books, must therefore have something of substance and value about them. Frankly, we flatter ourselves, and them.

A Passage to India, to which the plot of Atonement bears at least superficial similarities (a lie told by a young, impressionable woman, and the effect that this lie has on those around her), was rightly praised. Knightley, though, is no Judy Davis, and Ian McEwan is no EM Forster. Atonement is a perfectly fine novel, although it does not tell you very much about the process of atonement. Atonement is also, at times, a mesmerising and sumptuous spectacle as a film, while telling you even less. Yet the critics, with one or two exceptions, have jostled to lay garlands at its feet, to gush. An “awesome achievement”. It is, according to a compendium of adjectives from the Rotten Tomatoes film site, clever, ambitious, compassionate, stunning, intelligent. You diss Atonement at your peril; its supporters are legion, and armed with hurt and outrage. As are the anti camp, who hate it with a rare passion. Perhaps this battle is even taking place in your own household.

Oddly enough, the film it most recalled to mind, for me, was Titanic. Now this, I accept, is unfair. Titanic is possibly the most vapid and stupid film I have ever seen – you may be pulled in by its cinematic beauty, but you must surely be repulsed by the insultingly risible dialogue, by the acting, by the conceit. I have never before in my life cheered an iceberg. Atonement is not in remotely the same league of stupidity, but its determination to present a magnificent spectacle, at the expense of all else, is what remains with you once you have left the theatre. If there is an Oscar that Atonement truly deserves, it is for Seamus McGarvey’s extraordinarily beautiful photography; the film slips from one glorious portrait to the next, the cast always subordinate to the sumptuous surroundings. One moment a magnificent Turner seascape, the next a Monet lily pond, then, later, a horrifying triptych of Paul Nash on the battlefield: literally, in this case, all smoke and mirrors.

Lovely it undoubtedly is, but it also makes you disbelieve. Atonement is a less naturalistic film than Kill Bill or Cats & Dogs. The actors are dumped into the middle of these astonishing, painstakingly created tableaux and, prettily, do their stuff. If this is what is meant by “ambition” and “achievement”, then I would agree – but it is also distracting. And never more so than during an interminable tracking shot of Robbie wandering through the chaos and misery on the beach at Dunkirk, when you simply admire the technique and the mastery, and forget what is meant to be happening. Which is perhaps why, when the film is forced by McEwan’s novel to deal with complex emotional issues, it stumbles and our attention is lost. Romola Garai, as the repentant Briony Tallis, comforts a French soldier as he dies in hospital – but there is a blankness and emptiness about a scene that, in the novel, has power and resonance. And the whole point, one assumes, of the book is to reveal to us Briony’s later, flawed attempt at atonement – compressed in the film to one three- or four-minute, adequately acted set piece with Vanessa Redgrave.

I suppose Wright might counter that, since the film is a fiction, a fiction in the mind of Briony, the lack of naturalism and the overweening artificiality are there precisely to remind us, retrospectively, of this fact. In which case, we may feel a little cheated at the notion that all that has gone before was an extremely selective memory, gilded by expedient imagination. The book is, predictably enough, more nuanced, rather more sophisticated, about what is fact and what is fiction. Nor does it excuse the occasional lumpen cinematic clichés – Robbie walking among a field of (admittedly, beautifully filmed) poppies, all too many allusions to Christ, the repeated clacking of the typewriter keys to assure us that this is something that has been written, rather than actually is. Yes, we know all that, thank you.

Still, I enjoyed the film, although less than I enjoyed Dodgeball and Ice Age. My adverse reaction is more to the stuff that has been shovelled onto the film and, perhaps, its own pretensions. There are affecting moments, brilliantly executed, with an eye for detail: the merging of the soldiers at Dunkirk singing For Those in Peril on the Sea with a soundtrack that begins as a descant counterpoint and ends in the atonal; the blank-eyed, calculated spite of the young Briony, superbly played by Saoirse Ronan. It is a good film, I would not doubt that – even if, because of the need to convey emotional complexity, it sags somewhat in the middle. A good small film thinking that it’s a great big film, maybe. For great, you need more than mere beauty.

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