Everyone expects the Spanish Inquisition in Verdi's 'Don Carlo,' a work hailed as his greatest opera. All the classic operatic elements are there in plus sizes: love, betrayal, intrigue and the most dysfunctional royal family this side of the Pyrenees. Don Carlo's arranged marriage to Elisabetta de Valois was thwarted by his father, King Phillip II, who married her himself. Carlo had the bad luck to fall in love with his intended (and she with him), and in despair, he allies himself with the oppressed people of Flanders. 7:30 p.m. Thursday and Saturday at Music Hall.