Bernard Haitink, former music director of the Royal Opera, was given a hero's welcome as he took the podium for a revival of Parsifal. Now 78, he left in 2002 when the house was in turmoil and returns to a far more serene establishment - at least in the parts the audience see.

If anything this serenity hindered rather than helped the first night of Wagner's epic final opera. Singers, orchestra and audience were sorely tested by Haitink's more than ceremonial pace, which at times came close to stasis. For all the exquisite sounds from stage and pit, this Parsifal felt every second of its five hours 15 minutes and some. In part the fault was the low energy of this 2001 co-production with Teatro Real Madrid, directed by Klaus Michael Gržber. In terms of plotting a drama, few come more serious than Wagner.

You could make a contour map of this opera and find it bristling with incident, adventure and high peaks. Yet this felt like an unvarying plateau in which even key moments were botched. Has anyone, bar Dan Brown, ever seen a more underactive Grail? Parsifal's near-miss kiss with Kundry was positively Masonic in its reticence. And the Klingsor magic sword moment - pure theatre when done well - had one eye on Spamalot in its incompetence.

Nevertheless there were admirable performances, notably from John Tomlinson, returning as the veteran knight Gurnemanz. His wise presence can animate any stage, and did, though the slow pace put extra strain on his voice in this huge role. Petra Lang was bizarre and exciting as Kundry. Willard White's Klingsor, though mellower than of late, remains gripping. Flowermaidens and chorus deserve praise and Falk Struckmann mustered urgent pathos as Amfortas.

But all were under-charactised, especially Parsifal himself, who was forever hanging around or hiding behind a pillar. British tenor Christopher Ventris has the makings of a fine lyrical "Pure Fool", if only someone would direct him.

Haitink has described the text of Parsifal as "horrible". Given its sickly tangle of religiosity and disease, it is hard to disagree. But perhaps his lack of sympathy prompted an over-beautiful, languid interpretation, with the drama lost. It's too easy to say forget the words, just listen to the music. However repulsive, they make this maddeningly enigmatic work an opera.

• Until 21 Dec (020 7304 4000).