The Olivier and Award-winning success of The Play What I Wrote was always going to be a tough act to follow. That blissfully comic meditation of the nature of comic partnerships, inspired by Morecambe and Wise (who were never mentioned by name), proved also to be an infinitely touching series of theatrical in-jokes that sprang from the unique partnership that created the show, Sean Foley and Hamish McColl (aka The Right Size).

After 13 shows together in 13 years, this was the perfect distillation of The Right Size's way of constantly breaching the theatre's fourth wall as they showed a chaotic performance in progress. And into the midst of the self-referential nature of mayhem that resulted, a changing roster of celebrity guests was also pressed into its nightly service.

Now the duo leap onto the performance high-wire again, and go one stage further with Ducktastic. Conceived in part as a tribute to Siegfried and Roy - the famously cheesy Las Vegas magicians who worked with live white tigers until Roy was mauled and nearly killed by one in 2003 - this time The Right Size duly offer a whole menagerie of live (and a few animatronic) animals, plus a full supporting cast of six other actors. Wisely, as the title suggests, they've substituted ducks for man-eating cats. But, if some of us critics were dined on roast duck (care of the show producer) before the show, I'm afraid we were mostly served a turkey thereafter.

It may be as difficult to bite the hand that has literally fed us as to attempt to stomach the sight of a species we have just feasted upon before the axe fell on them. But despite the undoubted affection that McColl and Hamish inspire and the winningly unpredictable ways of the ducks themselves - one of whom was reportedly stolen from the dressing room two nights before the opening night - you can't help feeling wholly unfulfilled.

Goodwill will only go so far, though, and this show requires a lot more of it than I was ultimately willing to allow. Partly, it's a victim of its own excess. I sensed that, given the budget they were clearly afforded, with multiple set and costume changes, McColl and Foley's "rough theatre" magic was suddenly replaced by the kind of stunts that only money can buy. As natural successors to the epic-on-a-shoestring ethos of the National Theatre of Brent, winning this theatrical version of the lottery has stunted their creativity.

Worse, while the feeble plot barely holds together - as Sassoon (McColl), whose former magic partner and wife Judith has left him, conscripts Roy (Foley) from the audience, and a succession of vanishing tricks helplessly draw in other members of the 'audience' - the show becomes over-saturated in bad jokes and worse costumes, that variously turn McColl into something from an Abba band revival and Foley into resembling Woody Allen as a sperm suit from Everything You Always Wanted to Know About Sex But Were Afraid to Ask.

McColl's voice, too, is beginning to grate. It seems to be sustained here on single crescendos of rising panic that end in a desperate draw of questioning breath. He's probably wondering not just where the original Daphne the Duck got to, but where the show vanished to along the way.

- Mark Shenton