Deborah Voigt’s first Met Opera engagement following gastric bypass surgery is going well, and that’s no small thing, since “any surgery higher than the knees could, in theory, compromise the vocal mechanism… But in many ways, her dietary concession to the modern visual age turns out to be not all that artistically significant. She may land a few extra magazine covers, but what matters most are her detailed word coloring and inflection of the vocal line. Those strengths have come slowly to her over the years, but on Monday, she outran her costars in that respect. And that’s saying a lot.”