The Metropolitan Opera’s season kicks off with a mostly acclaimed staging of Wagner’s weepy, lengthy Tristan und Isolde. Counting intermissions this one runs close to five hours, but you’re free to tailgate during the intermissions. Soprano Nina Stemme and heldentenor Stuart Skelton play the doomed lovers, an Irish princess and the knight charged with delivering her to her new husband in Cornwall. Marisa Treliński’s staging starts off aboard a modern looking warship (complete with surveillance equipment) and ends very badly in a hospital ward. $27 seems expensive for something at the Showcase but by the third act you’ll be thankful for the cushy seating.