There is always a danger when employing famous artists to design theatrical sets that the visuals become the staging and what goes on within them becomes secondary – who, for instance, remembers the stage directors behind the productions famously designed by David Hockney (The Rake’s ProgressTristanDie Frau ohne Schatten)? But since Anish Kapoor’s creations for English National Opera’s new production of Wagner’s Tristan and Isolde are so much more physical than mere painted backcloths, they play a significant role in the drama itself.

For Act I Kapoor has designed a vast multiple sail-like structure, creating rooms fanning out from a central core like the segments of an orange (and it is indeed orange, or gold, in colour). We have Isolde’s quarters on the left, Tristan’s on the right, and the middle one remains dark until the arrival of the third party in this three-way relationship, King Mark, at the very end of the act. Act II is dominated by what looks like a rocky grotto, or a cave in the cliffs of Cornwall, perhaps, where the lovers have their tryst, turning at the moment of their discovery to reveal it is contained in a moon-like sphere. For Act III the grotto is partly screened from view and seen through a big gash that presumably represents Tristan’s wound. It all looks stunning, and is evocatively lit by Paul Anderson.

The production by Daniel Kramer, ENO’s newly appointed artistic director, is at its best when it engages with these impressive surroundings, taking us into the realm of the mind, away from the physical world – the Act II duet, with the lovers crawling around the pathways of the grotto, is a particularly evocative presentation and a magical fusion of sound and image. Elsewhere, his thought-processes are less clear. Flashes of insight – the lovers’ self-harming as indication of their death-wish, and the cumbersome dressing up for the arrival in Cornwall to meet the king revealing the social conventions that are about to be challenged – are counteracted by more inexplicable decisions. It’s reasonable to mark the lovers’ interruption with the cold light of day, but do they need to be strapped to modern hospital beds and tended to by massed medics while Mark gives them his poignant dressing-down?

And while on the subject of incongruities, what was with the Samurai allusions in Christina Cunningham’s costuming of Tristan, Mark and the ship’s crew in Act I, something that was never picked up on again? Otherwise, there’s a rather camped-up 18th-century presentation of the lead characters in this opening act, with both Brangäne and Kurwenal be-wigged as escapees from Ariadne auf Naxos, or equivalent, faffing around with their superiors’ clothing. The desolation of Act III is well presented, with the lovers white-haired, their servants dishevelled and almost bald, but the effect is spoiled with some unnecessary and intrusive comic business with Kurwenal. Tristan can work on stage as abstract music drama – its "action", as Wagner termed it, is all in the music and words – or as narrative realism. Rarely does it take easily to combining both approaches, as Kramer’s somewhat uneven presentation shows.

Fortunately, the musical qualities of much of this performance provided compensation. First among them has to be the Tristan of Stuart Skelton, who on this basis must surely be regarded as one of the finest Wagnerian tenors before us today. His tonal clarity, crisp diction, firmness and attention to the detail of Wagner’s vocal writing are rarely to be found in a single singer, and while his voice may have become a little more Grimes-like (one of Skelton’s other key roles) in his mad reveries of Act III, he is meant to be mortally wounded by this stage.

Heidi Melton’s Isolde began well, and her singing was refined and suitably projected in the more conversational passages, but there was a tendency for things to loosen too much when singing at full pelt, especially in the heated exchanges of the Act II love duet, and her Liebestod lacked bloom. Karen Cargill’s Brangäne was a beacon of clarity (Andrew Porter’s English translation is used), but Craig Colclough’s Kurwenal, often mellifluously sung, was hampered by his over-the-top characterisation, which at times gave one the feeling that he’d stepped in from an opera buffa by mistake. Matthew Rose’s expressive interjections at the ends of Acts II and III were sensitively and compassionately sung, taking advantage of conductor Edward Gardner’s slow tempi here.

Gardner had begun the work with a relatively swift account of the famous Prelude and while one wasn’t especially aware of anything dragging, final timings suggest it was a slower than average interpretation overall, yet one that was both searching and searing in its ebb and flow and often blazing in its high emotional temperature. Wagner has always brought out the best in the ENO Orchestra, going back to the days of the legendary Reginald Goodall (though I doubt if any players remain from his day). This performance lived up to the best of that tradition in the ensemble’s colour, translucence and sheer richness of sound.