Wagner's Ring, an everyday story of gods, dwarfs, naked nymphs and a magic crock of gold, is back at the Royal Opera House, the first complete cycle in a decade and the first in the new building. Gustav Mahler conducted Covent Garden's first Ring in 1892. Now the task falls to Antonio Pappano, at the start of his fifth season as music director.

In terms of Western art, this is the Himalayas, Karakoram and Andes rolled into one. For four nights over the coming week, a world-class cast and a huge orchestra including 18 anvils, six harps and a thunder machine, will perform 16 hours of music. Those lucky enough to have a ticket for this sell-out event will be in Wagner heaven or, for those unready for it, hell.

Never big on modesty, Wagner described the Ring as an epic tale containing the beginning and end of the world. The challenge is for lesser mortals - directors, designers, musicians - to bring the work to convincing life.

Director Keith Warner and designer Stefanos Lazaridis embarked on the production three years ago, with inevitable casualties on the way. The biggest loss was Bryn Terfel who pulled out, to some derision, at the start of rehearsals on account of his son's broken finger.

He was due to sing one-eyed Wotan, the chief god who over the course of the Ring sees his powers dwindle, usurped by man's supremacy. This is the essence of the Ring. Terfel was missed, but to sing this greatest of bass-baritone roles with his mind elsewhere would have been mad. (Overheard, on good male authority, at a urinal: "At least they've got rid of that bloody Welshman.") Who can complain at having John Tomlinson, with 20 years of experience, once more taking up Wotan's spear. Always best to have your heroes sung by heroes.

Much has changed since 2004, especially the lurid, human laboratory which is Niebelheim, a paradise for the perverted, with a necrophiliac rape and a few gruesome, flayed body parts. Fussiness remains but there is new clarity, especially at key moments: Alberich's curse, Wotan's lust for the gold. Special praise here for Franz-Josef Selig's tender giant Fasolt, felled by his greedy brother.

To hope for consistency in a work as grandly complex as the Ring is to bark up the wrong World Ash Tree. Das Rheingold is just the curtain raiser. Only at the end of the week will we know how these performers, and this ambitious production, make out. Pappano, at the curtain call, was covered in sweat. This trial of stamina is under way.

• Three cycles, until 2 November. Friday 12 October - Das Rheingold performance for students. Box office: 020 7304 4000