It lacks substance. The composers of banal music assemble its elements with no genuine feeling. As Wolterstorff explains, music with substance is internally rich, varied, and complex. It inspires us with its subtlety, contrast, and imagination. The most important concept in appreciating music is expressiveness.
Expressive music satisfies the concepts of unity and substance.
Likewise, unity and substance contribute to expressiveness. By expressiveness we mean emotional power. However, this doesn't mean expressive music is necessarily wrought with overblown emotions. The idea is that the expression is strikingly appropriate and relevant. These three general concepts can serve as a basic guideline for measuring good music.