Semyon Bychkov is making his Metropolitan Opera debut this week, 20 years after he seemed like the next hot conductor. What happened? “Bychkov’s career illustrates, among other things, the growing pains that take place in the trajectory from wunderkind to established maestro. At 51, with a mop of curly black hair, he’s still young in conductor years. But for conductors and musicians of his generation, those growing pains were exacerbated by the decline of the recording industry, meaning that big cushy recording contracts with major labels were not renewed. Meanwhile his newness wore off. Always a conductor with a certain amount of brio and showmanship, a crackling energy that gets the audience going, he is sometimes branded heavy-handed.”