In the old days harmony was a term employed to describe a beautiful melody... Terms have been changed...
We live in a time with huge variety so objective answers are very hard to come to. Western culture is very dynamic, grown more dynamic over the ages, and these days it came to the point we switch from one opposite to the other in a very fast pace. Yesterday this style appealed to us, tommorow its opposite.
When I think about this question in an abstract way beautiful and meaningful art is able to bring opposites together, in harmony, in good standing. The middle point between opposites is impossible to reach so we can dance around it, making the invisible unity clear. In this sense every artwork points beyond itself and can therefore the listener or viewer to come to a transcendental experience (although some works have this more than others since not every work makes this to its (main) aim). But because we can never reach this middle point perfectly since it never can be expressed through anything this leaves us with an unending series of works of art. Every artwork is limited by being an work of art! A paradox... I think a good artwork knows its limits and because it knows its limits all elements fall into a meaningful place. It's not only beautiful because it makes apparent what is beyond it is also beautiful because it is limited, in its humble existence so it can point beyond itself. Dissonance can help make things more beautiful when it is placed in the context of consonance. A good work of art isn't only pleasant but at least also a bit painful to experience because it is a testimony of life as it is. We humans have the capacity to appreciate this and find beauty in tragedy.
Some thoughts... A bit chaotic maybe. But you might find some things to think about.