Lang Lang/Tan Dun/LSO, Barbican, LondonImogen Cooper, Queen Elizabeth Hall, London

Tan Dun's new work may be ambitious, but pianist Lang Lang gives it more glamour than it's worth

Brand recognition is a term seldom used when discussing concert pianists, but Lang Lang has broken the mould.

In addition to CDs and DVDs of his performances, you can buy two versions of his autobiography and even a pair of trainers (the $125 limited edition Adidas Gazelles, with a gold and black piano motif on the outside and gold piano pedals inside). No fewer than five Lang Lang™ Steinways are available in China, where more than 40 million children are said to be taking piano lessons as a result of "the Lang Lang effect". As sparkly as a Swarovski concession in a Dubai shopping mall, as ubiquitous as Microsoft, the 26-year-old Unicef Goodwill Ambassador has become as popular as Ronald McDonald, with the bonus that he is unlikely to make you fat.

There's no doubting Lang Lang's technique, enthusiasm, energy, enterprise or commitment to music education. It is difficult to think of another pianist who'd find time for an appearance on breakfast TV during a Barbican residency of workshops, masterclasses, two concertos, an evening of East-West fusion chamber music and a solo recital. If his playing inclines to flashiness and emotionalism, he stands in the dock with the great virtuosi of the 19th century. Set aside the product endorsements and this is Lisztomania reborn. People love Lang Lang. But as the self-styled "big kid" from Manchuria recently admitted, "If the work is bad, there's nothing you can do." Actually, there is. You can choose not to play it. Except, of course, when you are China's most famous pianist and the work in question has been written for you by China's most famous composer, Tan Dun.

As revealed in the London Symphony Orchestra's UK premiere of The Fire, Tan Dun has not just turned his back on minimalism – he's gone into minimalism's closet, put prawns in its clothing rail and shredded its suits. What remains of his once-elegant, less-is-more, pre-Hollywood style is an unnervingly anorexic form of maximalism: something that speaks of big emotions such as aspiration, yearning or regret, in language borrowed from Rachmaninov and Ravel and cut into julienne strips. His piano concerto begins with seemingly idle strokes of one note of the keyboard against a series of Vaseline-smeared glissandi, before opening into an improbable love duet between pianist and timpanist. They've got history, is the implication. Things didn't work out between them and the memories are kinda beautiful, kinda sad, kinda Streisand and Redford in The Way We Were. Then, boom! We're into a chase sequence and it's Lang Lang as Steve McQueen.

A lone trumpet glows over the moonlit landscape of the second movement. Gongs shine, strings shiver, and the soloist is left to attempt to make something poetic from the musical equivalent of a melancholy marshmallow. To Lang Lang's great credit, he almost achieved it, playing with a crispness and subdued delicacy this score does not deserve. A noisy closing movement plunders Gershwin's skyscraper syncopations for second-hand glamour and, bizarrely, quotes the most famous of trills in the piano concerto repertoire (Beethoven's Emperor). There were many potentially final bars. So many, in fact, that I began to despair each time I saw Tan flip over another page of the full score. My relief when it ended with a crash of Lang Lang's elbows on the keyboard and another toe-to-top glissando was immense.

Of Tan's hubristically titled Internet Symphony Eroica, commissioned for the YouTube Symphony Orchestra but here robbed of its group-hug raison d'être, the best that can be said is that it is sincere. Very sincere. So sincere that were President Obama to broker world peace while delivering a baby, this would be the soundtrack. Poor LSO! That Daniel Harding's post-interval reading of Mahler's First Symphony sounded similarly flabby was not surprising: having heard so much pseudo-numinous kitsch before it, I too was suffering from a nasty hug-over.

Would Lang Lang attempt the all-Schubert programme Imogen Cooper gave at the Queen Elizabeth Hall the following night? It seems unlikely, though the tenderness and discipline he lavished on Tan Dun's banal borrowings would be better rewarded in Schubert's 16 Deutsche Tänze (D783). These little jewels are not difficult to play – they're background music for soirées – but Cooper treated each as a private miracle. From the sprung vitality of the Menuetto of the G major Sonata (D 894) and the sublime harmonic switchbacks and Lieder-like voicing of the Moments Musicaux (D780) to the heroic narrative of the C minor Sonata (D 958), this was playing of unfaltering refinement and complete engagement with the score.

Sadly, Imogen Cooper™ trainers are not, as yet, available.

Lang Lang's Barbican residency concludes today (020-7638 8891)