Music is in games by default. As developer, you are expected to have it there or you loose points.
Great tool for setting mood (or breaking it), tool for standing out (or for being gray average). Sometimes even worth listening to on its own (or turned off asap).
But its mostly just part of environment like those flickering torches and shadows they cast.
What if we make it more? Little experiment: turn up music with some beat and start your favorite action game. Soon, you find yourself trying to play in rhythm. Attempting to “dance with game”.
This alone can be turned to awesome games aimed at casual audience. Dance-Dance revolution. Guitar Hero.
Now we can sidestep. What can make online game pure hell? Lag and lagspikes. Inability to react can break even best team and guaranteed defeat.
To be continued.