Composed in 1906-08, cast in four books of three pieces each and running for almost 90 minutes, Iberia is not only the culminating achievement of its virtuoso-composer, Isaac Albeniz (1860-1909), but the unsurpassed masterpiece of the Spanish solo-piano repertoire. Debussy hugely admired the music's colour and evocative power; Ravel vainly sought the rights to orchestrate it in his own inimitable way. And Messiaen came to regard it as the very foundation of modern writing for piano.

As well he might, for this extraordinary music not only somehow synthesises a Lisztian brilliance and a Debussian resonance with a huge range of Spanish folklore and street material, but exploits the keyboard with an almost unprecedented fullness: the two hands constantly having to dart between different layers of texture, keeping them distinct through quick changes of dynamic, colour and touch, while sustaining with the most subtle fluctuations of rubato the melodic lines that float or dance through the middle. Only the most consummate technicians and poets of the keyboard can even get near this stuff.

Such as the French-Canadian pianist Marc-André Hamelin - or so one had thought from his appearances here in recent years, throwing off the most quicksilver flights of Alkan and the most ferocious concatenations of Stefan Wolpe with a seemingly infallible clarity and fire. How, then, to account for the creeping disappointment of his latest Wigmore Hall recital, of the complete Iberia? The stately simplicity with which he launched the opening movement, "Evocacion", and his exquisitely hushed final bars promised well enough.

But later, one realised that there had already been warning signs in the item with which Hamelin preceded Iberia proper: "Navarra", which was originally intended for Book IV but was discarded unfinished, heard here with a rhetorical new ending by the American composer William Bolcom. It was Hamelin's tendency to half-pedal everything and to bang, so that textures constantly threatened to blur in a cloud of less-than-controlled resonance that should have caused concern. There certainly proved to be a sad lack of compensating dryness, of crisp definition in the many guitar-like accompaniment patterns of subsequent movements.

Most grievous was the handling of dissonance, notably in the amazing multiple crushed-grace-note effects with which Albeniz colours almost every chord of "Lavapies", which concludes Book III: balanced with exactitude, they add a tingling astringency to the harmony; played clumsily, they simply sound like fistfuls of wrong notes - as they did too often in Hamelin's hands. Ultimately, whatever the passing felicities, it sounded like a reading that, overall, and by Hamelin's transcendental best standards, was simply not ready.