Of the music I listened to ten years ago, only one album is still in rotation. The rest of it fell away as, piece by piece, it started to seem shallow. In high school, I probably thought my parents didn't understand my music, since it wasn't from their era. Instead, it's possible they understood it better than I did.
Everyone has experienced this. Some works of art (like songs, books, or photographs) seem good for a while, then get boring. Some works get better every time you experience them. Others, less. Great art is anything that keeps getting better, even on the hundredth time. Such works have depth.
You can picture this effect as graph, for each work , of its reward versus the number of times you've experienced it. In addition to this "reward curve", there's an "effort curve", describing how hard it is understand a work on each experience of it. Your enjoyment of a book (say) on a given reading is, roughly, the reward minus the effort. This is a simple model (and obvious once stated), but keeping it in mind has helped my understanding of some things.
It's why old people listen to classical music: that's what has held up over decades of listening. The effort to understand a work drops quickly, while its reward curve rises continuously. If I start listening now, Mozart will supposedly sound better to me in ten years than it does today.
I say "supposedly" because you can't somehow measure these things in advance. In making the claim about Mozart, I'm trusting received wisdom, which is about all you can do. People who have studied a medium deeply are better at predicting what will hold up over time, but even they aren't great at it. (And of course, tastes differ.)
It also explains why young people don't listen to classical music: for now, other music has higher reward-minus-effort. Any pop song anointed by Clear Channel is intentionally designed to meet this criteria. It must require low effort on the first listen, because otherwise listeners will change the station . And it doesn't matter one penny how you'll feel about the song on the hundredth listen.
The novel Ulysses is known to be hard to read. If on the first attempt your reward is greater than the effort it took you, you've either had help understanding it or you're a language genius. So, for most, getting through that first read isn't worth it. This effect causes some otherwise intelligent people to dismiss the book as overrated or pretentious, perhaps claiming it's only talked about at all for what having read it says about the talker. On the contrary, devotees claim that the effort, though high, falls steadily, while the reward increases steadily to heights higher than that of any other book. So, the first reading is worth it if you're willing to read it again — a kind of amortization.
Finally, from fear of seeming unromantic, I want to point out what I'm not talking about. The model above says nothing about how to measure effort or reward, nor how to predict them, nor what should or should not be considering rewarding, nor about what art is important. It is ultimately subjective. Besides being able to explain some phenomena more confidently than I could before, its main effect has been to encourage me to try harder to like new kinds of art.
 Saying "for each work" is an approximation. There is some crossover between works that use similar technique or express things in a similar way. Hence the example of my parents understanding my music from high school, or why a surprising painting technique can seem powerful at first before starting to look cheap.
This is why pop music is never too innovative; it can be at most one step ahead of what the listener has already heard.