Newly married to a ballet dancer, Pablo Picasso turned to his hand to stage and costume design. Andrew Lambirth celebrates the treasures of a new exhibition at the Palazzo Grassi in Venice
Do we need another Picasso exhibition? Whatever else is going on, somewhere in the world there always seems to be a retrospective of the Spanish master who so radically changed the art of the 20th century.

Recently we've seen his sculptures in London, the early work in Washington and Barcelona, the portraits in New York and then Paris. Now there's a grand celebration of the years 1917-24 in Venice at the Palazzo Grassi, with a display of the ceramics planned for London's Royal Academy in the autumn. The Picasso industry is booming. Is all the fuss worth it?

The show at the Palazzo Grassi starts with the tremendous spectacle of the 1917 drop curtain for Eric Satie's ballet Parade, made for Diaghilev's Ballets Russes. Not many museums could display this huge canvas as effectively as it is seen here, hanging in the great atrium of the palace, viewable from different heights as you climb through the building.

The image of a group of harlequins and strolling players with a winged horse nuzzling its young is naturalistic enough, though flat, in the theatrical convention, with a matt, slightly dusty look (probably the effect of ageing on the glue-tempera paint). For Picasso it marks a return to the depictions of circus folk of more than a decade earlier, in his rose period. Was this a pause in his inventiveness? A side track? Reprising earlier achievements has a dangerous feel to it: too easy, too comfortable.

1917-24 are Picasso's theatre years, and see him travelling more than usual: to Rome, Barcelona, Madrid and even London, with Diaghilev's troupe. This is a different, post-Cubist Picasso, newly married to the ballet dancer Olga Koklova, and attempting a fashionable semi-bourgeois existence. Perhaps his art was to some extent on hold.

There are a number of straightforward costume designs on show here, in the making of which, it seems, Picasso had no need to show off, or simply wasn't tempted to experiment much. Were they just a job to be done? Never let it be said that stage design is a superficial art, but there is a suggestion that the entirety of Picasso's considerable powers were not engaged in these projects.

Still, there are plenty of good things. A short prologue of early work establishes the historical context. It is a pleasure to see again the biting yet elegant dry-point line of the 1905 Saltimbanques, and other images of that strange cast of extravagantly thespian characters. Some of the theatre work has a striking individuality. The 1924 studies for the curtain for Massenet and Satie's ballet, Mercure, reveal both mastery and concentration. Done in pencil outline with colour blocked in, they have all the spontaneity of a doodle, coupled with a rare breadth of decorative vision. The curtain itself (much smaller than the gigantic drop for Parade, but in the collection of the same museum, the Pompidou in Paris) has been newly restored by Fiat, leaders in arts sponsorship, whose flagship the Palazzo Grassi is. The curtain is, however, still fragile, and is displayed at an angle of 15 degrees from the upright, the better to conserve it.

One of Picasso's strengths was in his drawing, as can be seen in the half-done 1923 painting Harlequin. Only the face and the right shoulder have had colour applied to them, the rest of the seated form being wonderfully suggested through line and cross-hatching.

Compare the swift outlines of his pencil portraits: for instance, the great 1920 drawing of Stravinsky, and a similar study of Satie, both with their constantly redrawn contours. For sheer simplicity, there is a lovely little monochromatic oil sketch of the artist's son, from 1922. A swift drawing in Indian ink for Pulcinella (1920), is almost a cartoon, yet its nervy brilliance highlights its descriptiveness.

Aside from looking back to his own achievements, Picasso was aware of a change in general mood: a recall to Classical values. This exhibition is subtitled The Italian Journey, and it deftly chronicles Picasso's continuing interest in the art of the past, and in particular, Pompeian frescoes and Renaissance paintings.

In the requiting Neoclassical pictures, Picasso is prepared to be clumsy, as in the Two Bathers of 1921, where the features and limbs are merely roughed in. Obviously that was enough - there's no feeling of boredom in this picture. Picasso stopped working on it presumably because he'd solved the particular problem he'd set himself; he'd discovered his answer.

By contrast, he can be superbly delicate; look at the tiny 1922 gouache portrait of an adolescent dressed as Pierrot. From the same year and in the same fluent style is Family at the Seaside, in oil on panel. Add Two Women Running on the Beach, another gouache. All three are small, intense works that look monumental, and all are borrowed from the Picasso Museum in Paris (the director of which, Jean Clair, is also the curator of this exhibition). These paintings shape their own rich mythology.

The exhibition ends on a high note, with two young male bathers, set against the sea at Antibes within vaguely Neo-classical architecture, and called The Pipes of Pan (1923). Their solid figures appear to be made of some pink stuff, less flesh than candy or moulding wax. Yet they possess a massive and touching humanity that many more naturalistic paintings cannot begin to comprehend.

However, not everything is good. Look at the 1921 pastel studies of hands - the worst kind of poster art. And so often you sense how bored Picasso could get - leaving details or whole areas unfinished in order to move on restlessly to the next idea.

Throughout the exhibition there is a wealth of archive material, mainly comprising documents and original photographs. But one of the weakest points is the display of stage costumes themselves, awkwardly rigged up on rudimentary mannequins, and not at all shown to their best advantage.

Picasso was such a protean artist, with so many ways of enabling us to see things anew, that there can never be too many exhibitions of his work. We are still too close to him in time to get a proper perspective on his achievement. However, with each successive show we learn a little more. And in terms of visual pleasure, the Palazzo Grassi exhibition is a great joy.

`Picasso 1917-24: The Italian Journey', Palazzo Grassi, San Samuele 3231, Venice, daily 10am-7pm until 28 June