More sad news from shutterland: Excelsior, the highly rated New American in Back Bay, has closed. According to the restaurant's website, however, the space will reopen in the fall as a new concept: "The new restaurant will be more casual than Excelsior, while maintaining the highest level of food, wine and service. Several dining options will be offered, from casual supper and drink at the bar to a full dinner menu on both the first and second floors."