Oper Opis, Barbican Theatre, London<br/>The Snow Queen, Coliseum, London

After an opening that is, literally, well balanced, a Swiss collaboration descends into a free-for-all

With each passing year, its content becomes harder to define. Suffice to say that the single factor linking the wildly diverse events of the London International Mime Festival is that they generally take place on a stage (though, even as I tap these words, a memory stirs of something in a fish tank).

Whatever, the opener of the 2010 season decisively undermines every sensible definition of a stage, for the performing surface in Oper Opis, the latest work of Swiss duo Martin Zimmermann and Dimitri de Perrot, is perilously unstable. Balanced on a giant airbag, its plane tilts and slopes in response to who is standing on it and where. If nothing else, it's a nice metaphor for mental equilibrium. Want something badly, move forward to grab it, and it slips out of reach.

Oper Opis is a bit of a puzzle in itself. It starts as if it's going to be one of those cerebral shows whose creators (who invariably have maths PhDs) perform experiments in gravity and geometry. Pottery shapes are lined up to be toppled like dominoes when someone pops through a trapdoor. There are gags with sliding chairs and sliding people, and music niftily assembled from live, sampled sounds. It's neat, clever, fearsomely controlled.

But as more characters appear, it turns into another kind of show: messier, more human, even freakish. Extreme physical types recall old-school circus: a pneumatically plump girl who emits shrieks while jiggling alternate breasts, and a petite gymnast who is carried on like a plank and seems to know no fear. (I will especially remember her nonchalant squat, held high in the air by one foot.)

There's also a preening Lothario in a white Elvis suit and a beer-bellied slob whose jersey won't meet his trousers, no matter how often he tugs at it. There's a creature intent on wearing a hoodie in every way except that intended, to morphing effect. The mood is urban and edgy, the men slope up to the women and adopt chat-up poses, with no results. The only couples who get it together are some dancing chairs – a lovely moment, as the DJ scratches a faded memory of a Léhar waltz on his portable turntable.

Bizarrely, the last third of the evening turns into a different show again: pure acrobatic circus this time, superbly done. But however impressive the skills, the whole distinctly fails to cohere. It's all very well borrowing the clothes of Pina Bausch – the non sequiturs, the repetitions – but you need to have somewhere to go in them.

It's not often a ballet company is wrong-footed by the weather. But snow-fatigue was bad news for English National Ballet, reviving a major addition to its own-label catalogue. Who wants to watch fake flakes in The Snow Queen when they've been struggling through the real stuff all week? There are more lasting reasons, though, why Michael Corder's three-acter, based on Hans Christian Andersen's story, won't be ousting The Nutcracker as a seasonal staple any time soon. For all its fluency and clear story-telling, it's not jolly or varied or tuneful enough to entertain families, and lacks the choreographic daring that might endear adults to choruses of hanky-waving peasants, a reindeer in tights and a boy with a shard of ice in his heart. Its chief attraction, to my mind, is the chance of hearing its late-Prokofiev score, filleted mainly from his ballet The Stone Flower. Alas, its emotional high points don't always mesh with those of the new story. An elementary requirement, surely.

Mime Festival at various venues until 31 Jan (www.mimefest.co.uk)