The Museum of Art is located within the pedestrial mall area of Balboa Park, in a charming building. On certain Tuesdays of the month, you can visit it for free.
The gallery space is fairly small, and the exhibits do not rotate very often. On the upside, this means that it is a very manageable gallery, meaning you don't feel overwhelmed by too many works of art, or feel the need to rush through it in attempt to see everything.
This is not a modern art museum -- the most "modern" of pieces is from the early 20th century, with most of the art work collection dating much farther back than that. There is a fairly large religious painting section upstairs.
Architecturally speaking, the building is beautiful -- wide, open and very grand. There is an outdoor sculpture garden as well. The museum store has interesting books and souvenirs as well.