Breakin' Convention, Sadler's Wells, London

Breakin' Convention, the Sadler's Wells festival of hip- hop dance, is one of the theatre's big successes. The holiday weekend of performances, workshops and demonstrations gives the place a festive air, with wrist bands, crash barriers and long queues to get in.

The main stage performances are long and varied. There are many different troupes each night, from international headliners (Brazil, Japan, Korea and France, though oddly not many from America) to younger local performances. It adds up to an exuberant, accessible show.

At the same time, artistic director Jonzi D is keen to push hip-hop forwards as a theatre art. Introducing this year's acts, he puts a lot of emphasis on Brazilian troupe Membros, given the star spot on Saturday night. Their show Febre (Fever) came with warnings about adult content, and a plea to this audience to be patient with the slower, more reflective pace of the work.

Hip-hop, based on street dance, has instant impact. Speed and excitement come naturally in this style, which works brilliantly in music videos or in competitions. Turning it into a theatre art is still a work in progress.

Febre crosses street dance with physical theatre. The performers do dance, legs twisting and rocking, but they also do a lot of suffering. Kicking themselves into the air, they let themselves fall, with a flat heavy thump that makes the audience gasp. But there's a masochistic edge to this exploration of unhappiness.

The Breakin' Convention audience is knowledgeable, generous but not necessarily adventurous. When Cambridge group Sin Cru opened their dance with some modern dance posing, you could feel the audience's distrust. As soon as the dancers threw in some recognisably hip-hop steps, this public was readier to accept the experiments.

The French group Styl'O'Styl were, well, very French about it. The three dancers, in their neat sweaters, dance to a mix of jazz, while their arching poses tilt into Marcel Marceau territory. It's Left-Bank existentialist hip-hop; too long, but stylish.

The British popping collective UDP stalk through their moves, flipping casually from one pose to the next. The young British Urban Strides, led by the gleeful beat boxing of Experimental, simply dive through their moves, confident and bouncy.

Some of the strongest dancing came from the Russian group Top 9, who arranged their dancing into punchy sketches. In a typewriter scene, a dancer's moves are so precisely isolated that the effect is of flickering film.

For a show about change, Frédéric Flamand's Metamorphoses is weirdly short on transformation. Dancers come and go, wrapped in tape or plastic fronds. Even when they climb into the set's turning wheels, or put on headdresses, they don't seem much altered .

The Ballet National de Marseille, returned to open this year's Brighton Festival. Flamand uses Brazilian designers Humberto and Fernando Campana to give this show its distinctive look.

Their set is dominated by circles. Video projections appear on a round screen. Phaeton's sun chariot is a hoop trailing sheets of clear plastic. Arachnae's web is another ring, criss-crossed with webbing. When nobody's dancing around or through them, the circles hang there, looking ill-assorted. The lack of focus might be a result of the Campana brothers' inexperience as stage designers. But it matches an aimlessness in Flamand's production.

Drawing on Ovid's poem, Flamand chooses nine changes, starting with people emerging from stones and ending with Medea's rejuvenating spells. The production doesn't tell these as stories. You can guess at identities from the more explicit props, but the dancers aren't strongly characterised. The music, a patchwork of styles from Saint-Saëns to electric crackles, does little to support narrative, but Flamand is more interested in themes than in narrative.

Flamand's strongest choreography is in a series of duets that become trios. As a couple dance, a third waits crouching at their feet, suddenly joining in some complex partnering. I'm still not sure which theme or story Flamand was illustrating, but at last we saw one kind of dancing turning into another.

Brighton Festival continues to 25 May. www.brightonfestival.org