Raw

The second given meaning of "raw" in Merriam-Webster's probably best suggests this adjective's use in describing music:
"2 a (1) : being in or nearly in the natural state : not processed or purified (raw fibers, raw sewage) (2) : not diluted or blended (raw spirits)
b : unprepared or imperfectly prepared for use
c : not being in polished, finished, or processed form (raw data, a raw draft of a thesis)"
It would seem that "rawness" is perceived a positive quality in much popular music as it implies authenticity. .