The undisputed charm of London's loveliest spot for summer theatre - and best alfresco Pimms bar - can only go so far. For too long in this, Shakespeare's most sophisticated comedy, it looks as though the fairy lights in Regent's Park are on but no one's home. The loose Jazz Age setting is pretty but jokes are thrown recklessly away and depths remain resolutely unexplored. That interval drink, it seems, will never arrive.

But gradually, a transformation begins, creeping over the actors and the action in this narrative of missing siblings and mistaken identities, until Act Five becomes a veritable masterclass in how to handle Shakespearean denouements. This act, in which devices are explained and desires fulfilled, is notoriously tricky to bring off without the entire cast standing statically around in an expository semi-circle. Yet director Edward Dick keeps the surprises fresh while still retaining that edge of unease left by the wronged steward Malvolio's threat of revenge.

Feste's melancholy closing song about daily rain is cleverly turned into a dance at the wedding ball of the two couples, with candles flick-ering atmospherically in niches in the back wall.

That backdrop, of a decayed Renaissance palazzo façade, might be fine for candles but it's no use for the crucial first scene, in which the shipwrecked Viola decides to disguise herself as a man until she can find her beloved twin brother. The import of her transformation is thus lost on us, a fact with which Natalie Dew's Viola struggles constantly.

Janie Dee's nicely composed Olivia skips around like Twinkle-toes in a ballgown once she's discarded her mourning weeds but the evening's real joy lies with "the lighter people". Clive Rowe's Feste is a grandstanding, sweet-voiced delight, whose suitcase of jester's tricks comes complete with a cocktail cabinet. Together with Belch (Tim Woodward, too shrewish) and lovable silly ass Aguecheek (Clive Hayward), Rowe makes a whole lot of merry before Richard O'Callaghan's perfectly peevish Malvolio arrives to put a stop to all such cakes and ale-related frivolities.

• In rep until July 30. Information: 0844 826 4242, www.openairtheatre.org.