“In recent years, this most sumptuous of classical-music gatherings has reverted to its default identity as a parade of musical celebrities with no clear artistic destination in sight. Last year, though, the progressive-minded Austrian pianist and impresario Markus Hinterhäuser took over as Salzburg’s artistic director, and he is stirring memories of the festival’s most vital period—that of the nineteen-nineties, when Gerard Mortier presided over a superb array of provocations.”