'Bandstand,' an openhearted, indecisive new musical, wants you clapping your hands and clenching your fists, tapping your toes and blinking back tears. It is both a peppy celebration of can-do spirit and a more somber exploration of what American servicemen experienced when they marched home from World War II. Directed and choreographed by Andy Blankenbuehler, the Tony Award-winning choreographer of 'Hamilton,' with book and lyrics by the Broadway newcomers Richard Oberacker and Rob Taylor, and a 1940s pastiche score by Mr. Oberacker, 'Bandstand' is an undercooked slice of apple pie, served with a dollop of anguish.