THE METROPOLITAN OPERA opened its 126th season on Monday — Peter Gelb’s third as general manager but the first over which he has had complete control — with Puccini’s “Tosca,” one of the sturdiest and most beloved war horses in the operatic stable. This was very good news if you were the sort of traditionalist Met fan who could happily watch the old Italian repertory — “Tosca,” “Turandot,” “Madama Butterfly” — over and over again, and are not looking forward to offerings later this season like Janacek’s “From the House of the Dead,” an almost plotless opera set in a Siberian labor camp, or “The Nose,” Shostakovich’s adaptation of a story about a man who doesn’t have one.On the other hand, the Met’s new “Tosca,” directed by Luc Bondy and designed by Richard Peduzzi, mothballed the nearly 25-year-old Franco Zeffirelli production, which though baroquely overstuffed was immensely popular with audiences. “Tosca” takes place in some of Rome’s most famous landmarks, and the Zeffirelli sets made you feel as if you were…