Superheroes haven’t had an easy time of it in musicals. It’s a Bird … It’s a Plane … It’s Superman opened in 1966 to critical praise but public indifference, and then there was that little show about Spider-Man some seasons back. Add to this unlucky list Superhero at Second Stage, which at least invents its own superheroes rather than sullying the reputations of beloved ones. Further, it’s beautifully produced, assembled by experienced hands (book, John Logan; music and lyrics, Tom Kitt), and possessing several good songs. The trouble is, Superhero isn’t so much written as programmed.