World Piano Competition | South Bank Centre, London

"It's so subjective!" said one of the hard-core regular audience during the World Piano Competition over the Easter period. A piano competition is not a sporting event - like criticism, it's about character and imagination, so of course personal feelings are involved. Apart from points of technique, what needs to be assessed is breadth and depth of experience, and how they are communicated. Subjectivity makes it all the more interesting.

"It's so subjective!" said one of the hard-core regular audience during the World Piano Competition over the Easter period. A piano competition is not a sporting event - like criticism, it's about character and imagination, so of course personal feelings are involved. Apart from points of technique, what needs to be assessed is breadth and depth of experience, and how they are communicated. Subjectivity makes it all the more interesting.

The competition is held every three years and this, the fourth, was, as ever, masterminded by the Moscow-trained pedagogue Sulamita Aronovsky. Prizes of £12,000, £8,000 and £6,000, plus a network of subsequent engagements, were on offer. The 23 candidates had to give a 30-minute recital, including a contrapuntal work (such as one of Bach's Preludes and Fugues), a study by Chopin and a study by a Romantic or modern composer, a work from the Viennese Classical repertory, and a "character" piece - all from prescribed lists. Then they all had to give a 40-minute recital, supposedly a "balanced" programme of their own choice, though including one prescribed work. Only then did the jury choose nine semi-finalists, who each gave a 50-minute recital including one modern work and a major piece by Chopin - otherwise, they could play what they liked. At the final concert, on Saturday, three lucky pianists played a concerto. (Each had to prepare two, from which the jury chose.)

The fascinating thing was to witness how players blossomed, or not, after their first recital. Chiao-Ying Chang, a Taiwanese pupil of Christopher Elton, was dull in stage one, then played five of Debussy's Preludes so exquisitely in stage two, she raised high hopes, only to disappoint in the semi-finals, when she played sonatas by Haydn and Chopin with cool correctness. She won one of the four educational awards that can be made to pianists under 23, regardless of what stage they reach in the competition.

Another educational award-winner was 15-year-old James Willshire, who was very competent and very dull in both his stage-one recitals. He didn't reach the semi-finals. Can you condemn a player so young to artistic oblivion? Well, the gift of communication is granted players younger still.

One of the great discoveries was the 13-year-old Wen-Yu Shen from Szechwan (Sichuan), who has been studying for two years with Gunther Hauer in Karlsrühe, where he and his mother are supported by a German philanthropist. Shen made the Purcell Room's new Steinway sound more beautiful than any pianist because he never forced but set it resonating like a crystal glass. He revealed each piece of music as the composer wrote it, as clear as innocence, and with extreme economy. He obviously loved playing, and his teacher told me he does not know what it is to be nervous. One day, Wen-Yu Shen will have to make the transition to maturity, but for now, he plays like an angel.

The fourth young player to get an education award was 18-year-old Israeli Ran Dank, who looked lost when he came on to the platform but became a different creature at the keyboard - full of feeling and with a promising sense of panache. He will be interesting to hear in two or three years' time. I would have put him in the semi-finals before some of his successful rivals. And I would have chosen the Australian William Chen, a pupil of Christopher Elton. He had an infectious flair for performance and chose enterprising repertoire, such as Carl Vine's Sonata and Percy Grainger's paraphrase of Der Rosenkavalier.

In his second recital, the 20-year-old Macedonian Simon Trpceski adopted such eccentric tempi in Brahms's Handel Variations, that I was sure he would be disqualified. Fortunately, he wasn't, and he went on to give an astonishingly imaginative account of Prokofiev's Seventh Sonata in the semis, as well as a passionate rendition of Chopin's Funeral March Sonata.

For character and individuality, he was matched - in his own way - by the 21-year-old Israeli Inon Barnatan, another pupil of Elton. The only thing he lacks is complete security of technique, for he sometimes miscalculated his finger weight and let tone disappear. Yet his performance of Ravel's Gaspard de la Nuit was magical, and he caught the dramatic character of Ronald Stevenson's Peter Grimes Fantasy vividly.

None of which I detected in the playing of the Italian Luca Rasca, who never made an ugly sound but was vapid and colourless in Chopin's Op 10 Studies, which he cruised through facilely, and casual in Ravel's Valses nobles et sentimentales. Yet he went through to the finals. As did Martin Cousin, familiar from the last competition, in which he reached the semis. Cousin seems to need some new stimulus in his life, because although his handling of Rachmaninov's Second Sonata and Prokofiev's Seventh was masterly, a lot of his playing lacked imaginative spark.

As it turned out, Cousin withdrew from the finals because of illness. He was replaced by the pianist who won the next highest number of jury votes. The 20-year-old Finn Antti Siirala struck me as heavy-handed and rather dull throughout the competition, yet when called upon to play Brahms's First Piano Concerto with the London Philharmonic conducted by Alexander Vedernikov, he rose to the occasion and made a forceful impact. He certainly made a much bigger sound than Rasca, who played the same work efficiently but without any show of temperament. Trpceski, the other finalist, played Prokofiev's Third Concerto with an infectious sense of physical enjoyment.

But how, on the one hand, can you compare performances of such different works; and, on the other hand, assuming a varied programme was part of the exercise, why could Rasca or Siirala not have performed one of the other concertos they offered? Winner doesn't quite take all in this event, but for the record, Siirala won first prize, Trpceski second, and Rasca third. The audience liked Trpceski best. So did I.