What are the qualities that are desirable in a music critic (or a movie critic, or video games reviewer, or book reviewer)?
Generally, the very first thing we want is that they review music that we have a chance of listening to. Maybe we’re considering whether to buy some music, and need some help to make a decision. Or we’re looking around to discover new music that we might like. Or we’re already listening to the music and want to reflect on the qualities of that music.
That means that we want music critics who like some of the same music we like. And since music critics usually wish to reach a sizeable audience, that means music critics have to like a lot of different things. Their tastes should be eclectic. Or, if a critic’s tastes are more particular, there needs to be an easy way to match them up with an audience with similar tastes. Music genres usually fulfill this purpose. For instance, if a reviewer only really likes post-rock, they can advertise themselves as a critic of post-rock.