Gertrude Grob-Prandl's Isolde may lack a certain degree of nuance, but she compensates with staggering vocal power and reserves of energy that seem inexhaustible. Her laser-focused top notes alone make this performance worth hearing—one can only imagine the impact they had in the house. Rudolf Lustig offers moments of solid singing as Tristan, though he occasionally resorts to a kind of Sprechstimme to navigate the more demanding passages, revealing signs of vocal strain. The true revelation of the evening is André Cluytens, who leads the orchestra, soloists, and chorus in a performance that is both cohesive and inspired.