Porgy And Bess, Savoy Theatre, London <!-- none onestar twostar threestar fourstar -->

I'm in danger of becoming a bore, banging on about the spectacularly healthy state London theatre is in at the moment. But guess what? Another opening and, yes, another triumph.

"Electrifying" is an overworked word, but if ever a show merited it, it is Trevor Nunn's revival of the Gershwins' Porgy and Bess. The precise terminology to use about this staging may be a matter of dispute (is it opera or musical?) but there's no doubt that it is a masterpiece of the first order.

Nunn, who directed the full four-hour shebang in an opera house (Glyndebourne) in the mid-1980s, returns to the piece with the good intention of making it accessible to people who can't afford ridiculous opera-house prices. He therefore gives it a persuasive makeover as a musical. Gone is the recitative and in comes good, robust (and often witty) dialogue.

There is vibrant dancing that pulses with sassiness and sex. If I have a cavil, it is that there is such a thing as hyperactivity and that Nunn occasionally piles on the atmosphere (in the storm scene, say) and overdoes the cultural texture (the folks in Catfish Row always a-basket-weaving, or a-net-mending etc etc) to the point of faint absurdity. Less might be more and the adrenalin levels could do with coming down a notch.

But, oh, the sheer bliss of experiencing a work that is a succession of some of the greatest songs ever written. "Plenty o' nuttin'"? No, God's plenty - in music (here adapted by Garth Valentine) that fuses black jazz and the synagogue, spiritual and strut. The chorus work is out of this world in the reach of its understanding of the lamentation and resolve of an abused people.

The musical textures are of transporting beauty - whether the dreamy orchestral undertow in the world's most voluptuous lullaby, "Summertime", or the snaky seductiveness and percussive bustle of Sportin' Life's song of temptation "There's a Boat That's Leavin' Soon For New York".

Clarke Peters is wonderfully moving as Porgy even when under some vocal strain, and Nicola Hughes is fabulous as Bess. The great duets sound all the more touching for being crooned in what might be described as coiling, transfigured speech rather than belted out operatically.

How wonderful that London now hosts two great musicals about the black experience written by Jewish geniuses (the other is Caroline, or Change, by Tony Kushner, at the National).

To 31 March (08701 648 787); a version of this review has already appeared in some editions of the paper