Take a pinch of Riverdance, a slice of Stomp, throw in a dash of the Kodo drummers and the rhythm of a US marching band and you get the essence of Blast!, a wannabe world-beater in the musical theatre blockbuster stakes.

Spawned from the Star of Indiana Drum and Bugle Corps, a major player in the highly competitive (I'll take their word for it) Outdoor Pageantry World Championships, Blast! is a 68-strong company made up of percussionists, brass players and a "visual ensemble". Bringing the outdoor pageantry indoors, director James Mason aims to turn Superbowl half-time entertainment into a showbiz sensation.

The logistics are certainly impressive. As the serried ranks of trumpeters and trombonists weave in and out with military precision while adding in the odd dancey flourish - one of Blast!'s major selling points is its acrobatic horns - it's hard not to be bowled over by the sheer scale of it all. And the displays of synchronised baton, flag and rifle twirling and tossing are genuinely breathtaking.

But a collection of circus tricks, however polished, doesn't make for a concept. So Blast! takes us on a musical journey across the rainbow, illustrating the emotions of the spectrum (substituting black for indigo because, well, indigo would have been too hard) in a parade of music and dance routines.

When it works, as it does in the fiery red finale (all flaring flamenco nostrils and swirling ribbons) then you forget the shallow conceit that lurks at Blast!'s heart. When it doesn't, what you are left with is some rather distasteful cultural globehopping which throws in didgeridoos, Latin percussion and the odd spot of martial arts in a frantic search for the right note.

A boiler-suited Ravel's Bolero (even with the ghosts of Torvill & Dean hanging heavy in the wings) was near the mark but a sickly All-American take on Aaron Copland's Simple Gifts made the green section all too appropriately named.

The real curiosity of Blast! is that although it is so clearly formed on the playing fields of America, it gets its world premiere in London. With the perpetually pasted-on smiles of the young cast - you feel like you're face to face with the Happy Cult - it's clear that it's the performers who are having a Blast!, not the audience.

Until February. Box office: 0171-416 6075