We have a hypothesis, so let's use it. We'll begin by trying to explain some phenomena we frequently observe about art.
What all art forms share
Part of the problem with trying to decipher art as a whole is that art forms seem so different on the surface. What does painting have to do with music? What does dancing have in common with architecture?
But if you look at the elements of each genre as a building block to a memory, you can begin to see the commonality. Since it takes two pieces of data to form a new memory, we can look at each art form for ways in which it creates associations between unrelated items.
In drama, you're often given a conflict. One character wants something, and another character wants it, too, but for a different reason. The motivations are different, but there's a common desire. Your brain creates an association between the different motivations, and a new memory is formed.
Music composers often pair a major chord with its relative minor. Major chords are often described as sounding "happy", and minor chords as sounding "sad". But the difference between a C major chord (notes C-E-G) and an A minor chord (notes A-C-E) is only one note. By juxtaposing the C major chord with an A minor chord, the composer is creating an association: they're dissimilar because of the major/minor difference, but they're also similar because two of the three notes are the same.
That's what we're looking for in each art form: juxtapositions of opposites, differences between similar elements, paradoxes, repeated sequences of different elements, associations between items: unrelated pairs which are combined to create a new Animal Brain memory. For want of a better word, let's just call all these things patterns.
The role of emotions in art
Emotions do two things for us. They trigger automatic, physical reactions which keep us alive and breeding. They also serve to enhance memory formation. We're more likely to remember things that are associated with emotions. Those emotionally enhanced memories keep us from repeating dangerous actions, and give us incentives to repeat beneficial behaviors.
Although emotions are not essential to memory creation, they are a powerful enhancer. If the goal of art is to create new nondeclarative memories, the triggering of emotions is a very important tool in the process.
I don't think our physical reactions to art (clapping, cheering, booing, crying, toe tapping, etc.) are a factor in our judgment of the quality of art. I'd guess that quality judgments and physical reactions are two separate effects from the same cause.
Why art is so hard to explain.
You make a judgment about a work of art, and then you want to explain why you feel the way you do. The problem is this: the data you used to make the decision are not available to your conscious mind. The data that informed the decision are nondeclarative memories. They're locked up in your Animal Brain, and you can't query them.
Instead, you go scouring for reasons in your Android Brain's declarative memories, but that's not where the answer is. Your Android Brain may contain facts about the patterns in the artwork, but it doesn't have the actual patterns themselves.
You cannot know for sure if the facts in your Android Brain match the patterns in your Animal Brain. It's a bit like Schrödinger's Cat. There's no easy way to peek inside the box.
Clichés and "I don't get it"
A cliché is simply a habituated memory. It's something we've been exposed to so often, that we have learned to ignore it as insignificant, just as the zebra ignores the wind-blown grass.
The "I don't get it" experience happens when an artist intends for you to recognize a pattern, to make some association between two items and create a new memory, and you don't recognize the pattern or association. I call this unrecognition.
An artist has to walk a delicate balance between cliché and unrecognition.
My baseball limericks suffer from both these problems. The limerick form is quite clichéd. Most people know the meter and rhyme pattern, so it's hard to create a novel experience. And if you're not a baseball fan, you're unlikely to recognize the associations I'm creating by juxtaposing the attributes of various baseball players. The size of my audience is therefore quite limited. I'm doomed to mediocrity, at best. Oh, well. But speaking of mediocrity...
Great vs. Mediocre vs. Bad
The great works of art resist habituation. The patterns within them are so layered and interconnected that you can keep finding relationships between the details of the work, even if you experience the artwork many times.
Mediocre works of art, on the other hand, may work to stimulate us once or twice. But sooner or later, habituation sets in.
Bad works of art don't even work the first time. They're riddled with cliché and/or unrecognition from the start.
Different opinions about the same work of art
We're measuring the creation of nondeclarative memories in our Animal Brain. To create a new memory, you need two bits of data. The bits can come from two sources: the artwork, or previous memories stored in the brain.
The artist controls only one of those sources. Some brains won't recognize patterns in the artwork, others will. Some brains will see clichés in the artwork, others will find the same pattern novel. Our own brain participates in the measuring of the artwork.
For example, there are two songs about dying on Peter Gabriel's album "Up" which I find particularly moving: "No Way Out", and "I Grieve". The reason I find them so moving is because they trigger emotional memories of my own father's death. If my father were still alive, I doubt I would have had nearly as strong a reaction to the songs. Half the source of my emotional reaction is from the music, but half is from my own brain. The association between the two sources forms the new memory.
For this reason, it really doesn't make much sense to say a work of art is simply "great". You really need to say the work of art is great to somebody. Any general measure of greatness needs to include some kind of demographics and probabilities. Hamlet is unlikely to seem great to preschoolers. It is more likely to seem great to adults.
Rise and Fall of Genres
Each genre of art has its natural building blocks, its common types of patterns, for creating new memories. As artists explore these genres, the building blocks get used over and over again. So as a genre ages, it becomes more and more difficult for the artist to avoid cliché.
Eventually, the artists feel the need to break the boundaries of the genre. When this happens, though, the result is often unrecognition for the masses. The patterns become so complex that it begins to take a trained eye to recognize the associations the artist is making. At this point, the popularity of the genre begins to fade.
You can probably recognize this phenomenon in the histories of painting and poetry. The patterns of abstract paintings and free verse are much more difficult for an untrained audience to recognize than those of representational paintings or rhymed verse, whose patterns are more obvious.
Difficulty predicting future analysis of current works
I remember the first time I heard the music of Prince. It sounded so strange to me! Unusual rhythms, weird chords: I just didn't get it: unrecognition. Twenty years later, what seems strange that I thought Prince's music was so hard to comprehend. Those rhythms and chords are everywhere now: cliché.
The old artwork has not changed. Our brains have changed. And because our brains change, the things artists do to create associations will adjust to those changes. In turn, those adjustments change what kinds of patterns we recognize.
It's a cycle that is hard to predict very far in advance. Art history can turn unrecognition into attention, and attention into cliché, or vice versa.
Critics who hate everything
Some of us are more susceptible to habituation than others. I suspect that those members of the population at either extreme don't make particularly good critics.
If you are very difficult to habituate, everything will seem interesting to you. You're going to like just about everything. That's not very useful criticism. We need to know the difference between good and bad art.
If you're easy to habituate, you'll quickly build up a considerable library of clichés in your brain. Over time, you will become harder and harder to please. These types of critics should probably switch genres often, so they can work with a balance of novelty and cliché.