My mother hates metal, and she tends to dislike anything remotely heavy, with a few exceptions (all of which are early rock pioneers from the sixties and seventies). She focuses a lot on the 'mood' of the songs as well, so if she deems it somehow depressing, she probably doesn't like it. That's probably why she finds Pink Floyd "very disturbing".
My dad lives in a different province. Judging by the CD collection he sent me years ago, he likes a wide variety of music, but also avoids anything too heavy. He also likes Celine Dion. =/