Grace of Monaco, the opening film at this year’s Cannes Festival, was keenly anticipated - although not necessarily for the right reasons. Well before it made its debut, the question on everyone’s lips had stopped being, “Will it be any good?” and started being, “Just how much of a disaster can it be?” Monaco’s royal family had taken pains to condemn the screenplay; countless commenters had questioned the wisdom of casting Nicole Kidman, now in her mid-forties, to play Grace Kelly in her early thirties; and the film’s American distributor, Harvey Weinstein, had repeatedly postponed the film’s release, grumbling all the while that its director, Olivier Dahan, hadn’t made his vision accessible to US audiences.

As it turns out, Weinstein was dead right to have his reservations about Grace of Monaco, but dead wrong about it being inaccessible. Far from being a challenging art-house project, like Dahan’s celebrated Edith Piaf biopic, La Vie en Rose, Grace Of Monaco is a clunkingly unconvincing melodrama which, were it not for its A-list star and the golden glow of the lighting, would be indistinguishable from the cheesiest and most patronising of made-for-TV biopics. Whatever Weinstein may think of it, subtle it ain’t.

As the film opens, a news broadcast gives us a helpful potted history of Kelly’s family, her Hollywood career, and her retirement from acting to marry Prince Rainier (Tim Roth), whom she met, appropriately enough, at the Cannes Film Festival in 1955. We then cut to 1961, when Princess Grace is married with children - but the dialogue keeps on explaining who she is and what she’s doing. I lost count of how many times someone told Grace that she was playing her greatest ever role, but it wasn’t as many as the times someone declared that her life was (or wasn’t) a fairy tale. Watching Grace of Monaco is like watching a hundred-minute trailer: instead of having conversations, the characters simply say something that sounds important, and then it’s time for the next scene.

But despite these characters’ strenuous efforts, we’re never persuaded that there’s anything important about either of the film’s two parallel storylines. In one strand, Alfred Hitchcock (Roger Ashton-Griffiths) drops by to offer Grace the starring role in Marnie, thus tempting her to take a break from being a princess and a mother. In the other strand, Rainier is threatened by a French diplomat that if he doesn’t start taxing his citizens and handing that tax over to France, President de Gaulle’s army will invade his tiny principality.

There are three problems with these plotlines. The first is that they're so short of spectacle and conflict: in one of them, Grace talks to an avuncular priest (Frank Langella) in various darkened rooms, while in the other, Rainier frowns, waves a cigarette around and talks to his advisors in various darkened rooms. The second problem is that we already know how both stories turn out: it’s hardly a spoiler to say that Monaco still exists, and that Tippi Hedren took the lead role in Marnie. But the third, most significant problem is ... well, who cares about any of it, anyway? Would Monaco really crumble if its princess did some acting? And would it really be terrible if its playboys and tycoons paid their taxes? When Grace addresses a roomful of billionaires in the Monte Carlo Casino about the importance of helping the less fortunate, it’s tempting to point out that she could set a good example by pawning a few of her many diamonds.

Still, it’s during this long final speech that Kidman radiates humanity and charisma: otherwise, she has the stiffness and plasticky sheen of a Grace Kelly dummy in a cut-price waxwork museum. The film’s characters may keep assuring Grace that she was born to play the role of a princess, but Kidman definitely wasn’t born to play the role of Grace.


If you would like to comment on this story or anything else you have seen on BBC Culture, head over to our Facebook page or message us on Twitter.