The Metropolitan Opera's "Der Ring des Nibelungen," Richard Wagner's epic tetralogy, continued on the afternoon of April 18 with the third part of the saga, "Siegfried," in a, for the most part, exceptionally well sung performance, featuring the strikingly successful debut of German tenor Christian Franz in the killer title part.

Much of the first act is sung by two tenors in contrasting roles, the Aryan hero Siegfried and the Nibelung dwarf Mime, who raised him-and, misshapen and greedy, is one of the composer's notoriously anti-Semitic caricatures. Too often entrusted to singers whose voices are threadbare or quirky, these were, here, solidly sung by, respectively, Franz and, replacing the announced Gerhard Siegel, Robert Brubaker. Both brought nuance and sensitivity to their assignments, singing lyrically, even tenderly, or with unforced heft, as needed.

Franz sang gently of mother and of Nature, in scenes in Acts One and Two, but lent power and exuberance to the first act's climactic forging song, a formidable solo. He paced himself so well that he did not find himself at a disadvantage when faced, after two-and-a-half demanding acts, with a Brünnhilde coming on fresh and in full cry, even though some of the higher reaches of the role, in Act Three, may not lie within his optimal comfort zone.

The Brünnhilde, Iréne Theorin's instrument did not sound entirely centered at first, but she seemed to hit her stride more when she resisted Siegfried's advances ("Kein Gott nahte mir je"). Individual exposed forte top notes were still not well placed and I suspect that a high dramatic soprano is not truly hers to command. Theorin replaced Christine Brewer, who had withdrawn from all "Ring" performances.

Veteran bass James Morris conveyed serene nobility as the older Wotan, here called the Wanderer and about to abdicate his godhood, in contrast with the youthful vigor he projected in "Das Rheingold" and the defeat that marked his maturing "Die Walküre" deity. Morris generally dealt with old enemy Alberich and his brother Mime with joviality, albeit not entirely sincere, and allowed glimpses of his old forcefulness to emerge when he held Mime at his mercy, beneath the tip of his spear, before his first act exit, and when confronting grandson Siegfried, unaware of the relationship and brashly dismissive of the senior barring his way-someone he thinks he recognizes as his father's enemy, not as his parents' parent-in the gripping scene that confirmed the passing of the old order.

Richard Paul Fink continued to limn the role of the "Ring" villain Alberich in a true bass-baritone instead of a bark. John Tomlinson was the booming Fafner, the giant-turned-dragon. Wendy White, deputizing for Jill Grove, made an orotund oracle-out-of-touch of Erda. And Lisette Oropesa offered a gleaming soprano forest bird.

James Levine, presiding in the pit, allowed no more orchestral volume than his cast could cope with, without neglecting the score's tonal color and breadth, and unleashed a sumptuous sound from his players in the driven, fateful prelude to Act Three. Director Otto Schenk joined Levine and the singers on stage at the end and received a well-deserved ovation as his and designers Günther Schneider-Siemssen (sets), Rolf Langenfass (costumes) and Gil Wechsler's (lighting) "Ring" production, cherished for nearly a quarter-of-a-century, reaches its retirement.

Remaining performances of "Siegfried" are on April 30 and May 7 at 6 p.m. For tickets from $15 to 375, call 212/362-6000, visit www.metopera.org, or go to the Met box office at Lincoln Center. Also, look for $20 rush tickets at the box office only, sold on the day of the performance.