I guess my idea is somewhat like pusga's, but, different because something that really suggests music is bad is the simplicity of the lyrics, and by this I mean using language that is so basic, no metaphors, personifications, nothing interesting. meaning that its telling more of a story or something along those lines. it's irritating to describe and to listen to pretty much.
but, I guess that only goes for certain ranges of music, so, overall I'd have to say being generic is bad music. generic means the music has been heard thousands of times before with nothing new happening, and feels like listening to one track that was decent over and over again especially if you tune into half the radio channels in britain.
I guess generic stuff just doesn't sound good to me, meaning it defeats the point of music. although there are others who just hop aboard to listening to one genre because of one catchy chorus.
tl;dr mainstream and generic music grumble grumble