"In many ways, the work of a critic is easy. We risk very little yet enjoy a position over those who offer up their work and their selves to our judgment. We thrive on negative criticism, which is fun to write and to read. But the bitter truth we critics must face, is that in the grand scheme of things, the average piece of junk is probably more meaningful than our criticism designating it so. But there are times when a critic truly risks something, and that is in the discovery and defense of the new. The world is often unkind to new talent, new creations, the new needs friends."
Anton Ego - from Ratatouille
It seems to me that artistic criticism has two purposes. The first is essentially didactic; to identify the artist's mistakes to help him or her improve. The second is evaluative; to determine whether the art is "good" or "bad" and how it deserves to be ranked in comparison to other works. The value of didactic criticism is obvious but the worth of evaluative criticism is less apparent. Why do we need to classify art as good or bad apart from whether it's popular?