If you are curious about zarzuela (the typical Spanish operetta) you will enjoy Amadeu, which tells the life story of Amadeo Vives, one of Spain's most famous zarzuela composers. The production is directed by Albert Boadilla, perhaps Spain's most distinguished theatre director. 21st January-13th February 2011, Sala Roja. Tickets are available from the website entradas.com and cost between 19€-40€. There are some discounts available.
Here's sneak preview of the production: