Conductor Valery Gergiev was greeted as a star at the Metropolitan Opera when he first arrived. And the reviews were terrific. But “in recent seasons he has had tense relations with the Met musicians and choristers, who are from all reports dismayed by what they consider his idiosyncratic technique, lack of focus and penchant for showing up late to rehearsals. That tension, and even hostility, showed. What is going on? Few artists have risen so fast at the Met.”