Can we use beauty as a valid criterion in evaluating art?
Interestingly, when scientists prove a theorem, they consider the beauty of a mathematical proof as a fundamental test. Neurologists claim that the same brain area that reacts to music and art is stimulated in a scientist encountering an elegant mathematical proof.
There is another definition of good art though, that of Henri Matisse:
"Art should be something like a good armchair in which to rest from physical fatigue."