"Good Art" - Here is a phrase as contentious a subject as religion or politics.
Neophytes who rant about art, having never studied it, are a source of frustration to me. Visual art, as any subject, requires extensive study to be understood and, as with any major field, it has so many branches and types that one could never 'finish' learning.
To have a base knowledge of visual art, one must study at least some of the history, gain a comprehension of the elements of design, learn a variety of media and techniques, gain a base understanding of science, physics, geometry and mathematics, and, most importantly, one must learn to take the time to see. One must view art as it exists everywhere naturally and as it is when manufactured through a unique human viewpoint.
Please remember, next time you are in front of a piece of art, contemporary or otherwise, while you may find it visually appealing or repulsive, you may benefit from learning what led to the creation of the piece before you are able to pass intelligent judgement on its validity as an art object.