Comment 28 by Functional Atheist :

One simple, objective point regarding attempts to quantify qualitative measurements of artistic value is durability through time. If significant numbers of people are still listening to a composer long after he or she is dead, that is an objective and suggestive data point. The same might be said of writers, painters, sculptors, and scientists. The likelihood that Shakespeare, or Leonardo, were truly brilliant in something like an objective sense is greater than the likelihood that Vladimir Nabokov or Jackson Pollack were. All of these people are dead, but Shakespeare and Leonardo have been dead much longer.

Time also provides context, and allows for faddish style points to become less important. Part of the esteem heaped on the Beatles can be attributed to the fact that large numbers of people are still alive who experienced the frenzy of Beatlemania, but within a few decades that will not be the case. My bet is that Beatles music will still be revered past the death of their last first generation fan, but right now that is a probabilistic hunch rather than a demonstrated fact.

Fair enough. That's one criteria: popularity over time. If a bawdy beer-drinking song is still sung in 200 years by 1001 people, it's a 'superior' piece of music to an obscure Wagner opera that's the same age, but only enjoyed by 1000 people.... ? The term 'instant classic' is an oxymoron then. We must withhold judgement on all new release artworks, considering them equally valid until age wearies some of them. Certainly there are plenty of Best Picture Oscar winners from the 1950s and 1960s that no one watches now, and other movies that were ignored at the time are now cult classics. That criteria forces one to take interesting positions, rejecting paintings of great technical virtuosity if they languish in unseen galleries.