but I'm not sure how to compare Renaissance art to Postmodern art objectively

But isn't this a quintessentially postmodern stance to take toward art? And all the more ironic because saying "there can be no objective statements about art" is an objective statement about art?

probably misses the point of art altogether.

Does it though? If art is solely about personal pleasure and emotion, then is Honey-Boo-Boo a superior piece of comedy to [insert high brow comedy here]? Is The Room better than Hamlet if I enjoy it more? If we take seriously the assertion that the two can hardly be compared, I think that is missing the point of art. To say that there is no good art or bad art, that there's only "what I like and what I don't like" is the narcissistic credo of our age as applied to art. I think that's...disturbing.

I'm not trying to pick on you, and I know it probably sounds like I'm being flip or curmudgeonly, but it's only because these are questions I take pretty seriously. It disturbs me to no end that we're sprinting toward a culture that doesn't appreciate any sort of objective stance about anything, even the most basic facts about the world.