In a non value-laden way, quality is contrasted with quantity. Something qualitative can be described but not enumerated.

When you use the term high quality (or imply it, as is the case in this thread), you're doing nothing but making a relativistic statement.

So, we now face the vagaries of defining a word that specifically denies strict definition.

I think you can use quality as a proxy for other quantifiable or definable things. For instance a pitcher with 250 strikeouts, 20 wins, and a 1.50 ERA has a quality season -- but you're still defining quality based on relativity -- good numbers with respect to bad numbers.

When it comes to quality artwork, you have the vagary of the word quality now superimposed on the vagary of the word art. It's compounded error.

No wonder there are so many different definitions here; and no wonder quality is in the eye of the beholder.