what is the difference between good and bad music


my friend says rap is bad music. another friend says mahler is a terrible composer.

is it all subjective, i.e., a matter of opinion ? or are there standards which can distinguish good from bad music, however one defines these terms ?

if there are standards, can one specify them or refer me to a source ?
mrtennis
Good music sounds good, bad music sounds bad.

I hope that clears things up.:-)
Post removed