This season Tristan has returned as a vehicle for Deborah Voigt, who sang her first Salome in the house two years ago. She appears in the production by David Hockney originally conceived for the Los Angeles Opera in 1987. The artist’s creation of child-like fantasy worlds can be effective in an opera like Turandot. But there is no more adult work in the repertoire than Tristan, and Wagner’s drama was not well served by these sets and costumes. The saturated primary colors, the cardboard cut-out swords, the Christmas pageant king – I found all of it a fourth grade distraction from the musical and philosophical seriousness of the piece.