Setting aside the question of taste, there are factual criteria.

A singing style which damages the voice is bad.

A playing style which damages the listeners' hearing is bad.

If A sings something, listens to it, and says, "I wish it hadn't come out sounding like that," then that's bad.

Gimmicks which are performed merely to grab attention rather than to give pleasure or communicate, are bad. I'm thinking here of music on radio, etc, where they know people are working and they wish to get the listener to notice the radio so as to hear the next commercial. I believe this explains the yowls, yips, wails and gurgles so prevalent in pop music.