Dynamics
The dynamics of music are those differences in the loud sounds and the softer sounds. The instrument sounds in a song can only have a limited level in the sound field of the mix so as not to over power everything else.
One or two genres that can give you the best experience in dynamics of songs is classical music & Jazz. These genres are not the typical nonstop banging you over the head, no rest type of music. With classical you can hear an feel the fluctuations of loud to soft throughout a classical piece. It can be a thrill of an experience because their is emotion in these differences.
You can also hear these differences in dynamics in movie soundtrack scores. This is what makes movies so magical. Those dynamics in the music along with the action on the screen really intensify the emotional involvement of the audience and the film.
Just imagine some of your favorite movies without any dynamics let alone a sound track. It would be either a weird, irritating, or dull experience. Unless you like the steady nonstop buzz of a beehive or constant ring of an alarm clock, listening to non dynamic sounds can be a test of tolerance I guess.