Covers non-combat gameplay, and how well the game interfaces with the player. This covers a lot of different values. How well you're put into the hero's role may also apply here. This covers the actual game music, as well as sound effects. Generally there will be about 10-15 unqiue scores to a game.
Good music is enjoyeable to the ear and adds another depth to the game.
Music can, for some people, make or break a game. Every noise coming from the game now falls under this category. This one's sometimes easy and sometimes hard. It is highly original, but it's done repeatedly, so it could be seen both ways. That doesn't belong in a review.