La Traviata stands or falls on its lead singers and in Norah Amsellem and Rolando Villazon this 2005 Salzburg Festival performance has a pair whose electric interactions and brilliant singing are irresistible. If Amsellem can't quite provide the vocal bloom of the great Violettas of the past, hers is a lovely voice used with intelligence and dramatic intensity and she has the coloratura chops to d