A Portrait of the Art

I am making progress on a Standard Model of elementary characteristics of good art. I have:

consistency

subtlety

effortlessness

A high-quality piece must be self-consistent; it must be subtle in its themes and artistry, although overt or abrasive style does no harm; and it must be made with a high degree of effortlessness, which is on the part of the creator and not necessarily the audience.
This last subject explains why practice is completely essential to the artist. He or she must develop a cognitive routine in piecing together the unit, such that stifling intentionality isn't required at each step, for that makes impossible cohesiveness of the whole.

Can accessibility be amended to the list? As mentioned earlier, it need not be easy on the part of the audience, but isn't it necessary some relation between the art and some conscious observer? Must good art be accessible to at least some sector of the cosmic sentient population?
Must good art be accessible to not all of the population? Can good art exist in relation to all?
Or must it exist in relation to all?
No-- accessibility is the only fair candidate here. I will ruminate over its merit...



Revision: These three characteristics are not requirements for high-quality art, as implied. They are elementary pieces that add to the quality, and they are the only ones I can presently identify.