I am afraid to listen to the Great Fugue. I would come to like it, whether it is great art, or whether it is pretentious garbage. That would not rule out any of my theories. How can I figure out which it is before listening to it repeatedly?

Do you want to know enough to administer a musical taste test for this?

If you give people links to two fugues (unlabeled and untitled at the link source), and do not tell them which is which, and they aren't familiar with either, enough responses of which is better might give you at least a rough idea of to what extent it's actually great or whether it's just riding on reputation. Although, if they've heard either, we would need to discard their results because of likely bias.