EITHER seasonal goodwill or too much seasonal booze persuades me to give a charitable thumbs half-up to the Royal Opera’s new Barber. It’s a pleasant enough three hours, especially with Rossini’s ebullient score fizzing along under Mark Elder’s revelatory direction. But with this quality of cast, the show should have been sharper and funnier.

The problem is that the directorial duo, Moshe Leiser and Patrice Caurier, seem besotted with the smarty-pants academic theory of “meta-theatricality” — the notion that the characters in a comic opera such as Barber actually know that they exist only in that medium, so the way to reach the heart of such operas is to emphasise their artifice and unreality.

Hence the decision that Figaro (personable George Petean) should make his first appearance through the stalls, attempting to hurl out one of opera’s greatest entrance-arias while hobnobbing with the punters. Hence, too, his stage-manager-like inspection of the footlights in the last ensemble, where he straightens the one that Joyce DiDonato’s Rosina had petulantly kicked over earlier.

And hence Agostino Cavalca’s strenuously eclectic mishmash of garish costumes, and Christian Fenouillat’s stage-within-a-stage set: a pastel box where even the windows and doors of Bartolo’s house make stagey entrances and exits.

Of course, that reflects Rosina’s trapped circumstances. But it also underlines the idea that this is a self-enclosed world cut off from real emotions. So when Rosina smashes up the furniture during the storm, there’s a sense of a frustrated, deceived woman’s genuine feelings breaking through, only to be as quickly stifled by the convention of the happy ending.

That is the evening’s best ten minutes, and it caps a mesmerising performance by DiDonato, who flaunts spectacular technique in Rosina’s quicksilver runs, along with a luscious tone and a ditsy personality that is a bit Lucille Ball in places, but not cloying. She is matched for quality by Bruce Praticò’s Bartolo — a wheezy, hideously porcine creation who nevertheless sings his patter with the crispness of fresh toast.

There are also lively performances from Raymond Aceto’s barrel-voiced Basilio, Elizabeth Gale’s splendidly bitter Berta and Toby Spence’s boyish Almaviva, though his voice took a while to settle. But the trouble is that once we get past the blissfully surreal opening — an entire orchestra, plus instruments and wigs, crawling pianissimo across the stage — and grow accustomed to nearly everyone in the cast wearing a false nose, there simply aren ’t enough laughs. Which is unfortunate in a comic opera.

There is, however, one undeniable coup — in the Act I finale. It fits the music’s helter-skelter momentum perfectly, and is genuinely startling, so I won’t say any more. Except that if you are prone to seasickness, look away.

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