The Robert Wilson 14 Stations is in itself worth the price of admission, but there is also a great Guston show (on Richard Nixon!).
For a great day, visit the Klimt exhibition at nearby Clark Art Institute, then see the survey of new art from Vienna at MASS MoCA. Hoffman gets digitized. (A discount package ticket for joint admission is available, but it's not well marketed, so you'll have to ask.)
Pros: family friendly, stunning art, great shop & cafe