Everybody listens to the same piece of music. Everybody approaches it from a different angle, but no opinion is any more or less valid at the core. What raises one's opinion's value is the knowledge and understanding attached to it. One who is able to critically analyze a work for what it is objectively has a more worthwhile opinion than the average teeny bopper. What raises the value of one's opinion on a specific type of music is not whether or not they like it, but whether or not they know and understand it. There are objective measures of quality, but they're obviously subject to opinion. You can judge how effective the artist is in communicating a message, the production, the instrumentation, the vocals, the dynamics, the songwriting, etc., but everyone will view these objective measures subjectively. Being that there are objective measures regarding quality, the more 'qualified' one is, the more relevant and valuable their assessment of a work is. The average music listener does not have a very worthwhile opinion as far as judging the quality of a work is concerned.