The categories of quality can only be part of the painting and could not have any relation to an outside system of value, like for instance the question of taste, modern or contemporary; aspects of technical and social development. Therefore such an outside body of reference is herewith dropped immediately.
We need to focus on what is used in the painting, how this tools are used and then how this corresponds with the subject and its representation.
The two technical categories are first, the drawing, or calligraphic body, second, the colouration or use of ink shade. They together form the more intellectual category of the composition, the arrangement of the displayed subject in the two dimensions of the painted area, usually with a clear intention to create a certain imagination of space.
Lets first talk about the calligraphic body of the painting.
One painter might be famous for his drawing like Dürer, another for the intriguing use of his colours like Patinier, a landscaper who fascinated Dürer, and according to his strength the painting is following the preference of the painter. For Japanese and Chinese painting the calligraphic body is the more important category when we determine quality. Many paintings might have no colours and not even ink shading, its black and white substitute.
To have a good starting point we should discuss first calligraphy, the brush written characters.
Here quality is determined by the distribution of unused and used space, in the characters and their placement on the paper, created with a free movement of the brush.
This tool is a rather long haired brush. Just to use it, one needs the right handling and a lot of practice. But to master it.....
Without thorough training how to write with the brush, it is very difficult to establish an understanding for the movement of the brush, represented by the strokes or dots on the paper.