Now in its 20th season, Leon Botstein’s annual symposium-cum-festival SummerScape never fails to mount a substantial operatic rarity. This year’s entry, which runs July 21 to 30, is Henri VIII, by Camille Saint-Saëns, a forgotten sequel to his hit Samson et Dalila. But the marquee composer this year is Ralph Vaughn Williams, whose delectable, all-too-rarely revived Sir John in Love, receives a concert performance on August 13. It’s a golden opportunity to hear a Shakespearean opera that sticks closer to the Bard’s language than most. Interwoven Elizabethan tunes like “Greensleeves” are the icing on the cake. —Matthew Gurewitsch