What is it that comes to those that wait? Joy, pure joy. London has waited a long time for Mark Morris - it was said there was no venue big enough, good enough or available - but the combined forces of Dance Umbrella and English National Opera have finally put things to rights. On Thursday at the Coliseum, the 24 members of the Mark Morris Dance Group hitched up to ENO's chorus, orchestra and soloists for Morris's choreographed version of a gem of the English baroque. It was a marriage made in heaven.

The American choreographer is fond of saying that he has learnt more about his craft from his favourite composer, Handel, than from anyone else. And L'Allegro il Penseroso ed il Moderato, Morris's dance work set to Handel's ode, set to Milton's poems, has become something of a company calling card. It was already well travelled when it was the hit of Edinburgh in 1994, and now we see why. The music is a perfect spur to Morris's imagination, not just for its formal structures - the recaps, retrogrades and canons that provide a satisfying geometry for movement. His dances seem to penetrate the very essence of baroque music - its capacity to encompass moments of grand introspection alongside an almost childish delight in simple things: the imitation of a pack of hounds, a shepherd's call, a skylark's song. Poetic notions of innocence and experience gain physical shape and form.

The 30 short dances that make up L'Allegro track Handel's recitatives, arias and choruses with an explicitness that is startling, touching and sometimes also funny. To depict a hunting scene, dancers bunch together on their knees raising twiggy arms to make a hedge. The "hounds" scuffle round it, one of them cocking a leg before racing after the quarry. At mention of flowers, dancers stand still and splay fingers round their faces as petals. References to sleep show couples not just supine but rolling earthily on and off each other's bodies ranged in a huge circle like a clock face. At one point each slumbering man is carried, foetus- curled in the arms of a female partner. Women hug women, men hug men. Such wholesome images beam through Milton's descriptions of 17th-century pastoral life as a new order meeting the old.

In Morris's modern dance arcadia nymphs don't shy from frollicking, yet the effect is never sugary. Milton's "Come and trip it as you go/ On the light fantastic toe" (or "toe-ho-ho- ho-ho" in Handel's chuckling torrent of notes) prompts a puckish male solo, scintillating in its toe-twiddling buoyancy, yet also a little arch, detached from its own high spirits as if to say, this is what it feels like to be on cloud nine. I challenge anyone to watch with a straight face and a dry eye.

Morris's set designer, Adrianne Lobel, dresses the huge Coliseum stage in five receding prosceniums, each equipped with coloured screens which change the frame of each dance like a giant Mondrian painting: strips of vivid mauve, mustard and cerise for one; a palette of misty greys for another. Gorgeous lighting makes the dancers' dresses glow like coloured lamps. Under the baton of Jane Glover, the ENO contingent - the whole lot of them, chorus, full baroque orchestra, soloists, too, democratically crammed into the pit - gave a crisp, cleanly contoured account of the score. Soprano Susan Gritton's stratospheric lark was sweet enough to make our own hearts sing as the dancer on-stage quivered and fluttered her transferred thoughts.

Morris's dancers are famous for not looking like dancers. Some are gangly, some are short, some are almost plump, and this diversity sits well with the grounded-but-graceful amalgam of folk styles that feed into Morris's steps. This is modern dance so accessible it makes you want to tip up your seat and join in. But the simplicity of Morris's walk-through human chains is merely the surface feature of a well that runs deep, plumbing connections between movement and meaning that are universal, profound and for the audience perhaps even unconscious. Towards the end of L'Allegro waves of dancers run upstage at full pelt, criss-crossing each other's paths to within a hair's breadth. On the closing cadence, the dancers mesh into three concentric circles, spinning like the turning world.

Afterwards in St Martin's Lane a Japanese student, almost speechless with excitement, rushed up to beg for my spent ticket to use for autographs. It had been, he said, a revelation. "Young people just don't know about this!" he cried. "I will tell all my friends!" Yes, tell your friends. But they'll need all their wiles to get a ticket. In an ideal world we would build a huge theatre to house regular visits from the Mark Morris Dance Group (the new Sadler's Wells is getting there). And issue tickets on the National Health.

Coliseum, WC2 (0171 632 8300), to Tues.