Art experts and educators such as Sally Hagaman have rather specific definitions of aesthetics:
There still is confusion between understanding aesthetics as an adjective (as in “aesthetic scanning”) and aesthetics as a noun (as in the philosophy of art), a distinction made clear years ago by Sharer (1983) and others. Aesthetic scanning clearly is a method of art criticism, of responding to a specific work or body of work. Aesthetics historically is a branch of philosophy with its own substantive content. This content deals with general questions about art such as “What is art?”, “What’s the difference between a work of art and a copy?”, “Are there criteria that can be used in evaluating all works of art?”, and “Is the concept of originality in art a meaningful one?”
I refer, more simply, to aesthetics as the process of recognizing and articulating the emotional and/or psychological response(s) to works of art.
You have to first recognize or identify the responses that you as an individual have to artworks before you can talk about them and use them to exemplify, define, defend, or otherwise discuss art (works) and Art (in general) in terms of “good,” “bad,” or the bigger questions Hagaman stated.
Most of us, sadly, have not been taught how to do this.
Schools, with their ever-threatened budgets for the arts, may teach us how to mold clay, encourage us to express ourselves creatively by drawing, give us plenty of time to master the techniques of plastering tempera well enough for cheerleaders to make those banners on brown craft paper, but they typically fail to give us insight into how we react to art.
This is why I like to take my kids to art museums, one at a time, giving them my undivided attention and helping teach them to how to think about and talk about what they like and don’t like. (Always illuminating!)
It’s not good enough to say, “It sucks,” or even, “It doesn’t speak to me.” Or to even feel that way. I want them to know why they feel it sucks, why it doesn’t speak to them.
Knowing why you feel the way you do about art is the only way you really know your own opinion — and feel comfortable discussing, buying, viewing art.