All rules have three parts. The first is the style of the writer. One of any author's greatest strengths is his ability to write directly to the taste, understanding and needs of his audience. That writing style is common to all successful products in the role-playing genre, from novels to computer games, and has nothing to do with content. The second part of a rules book is content.
Content has two aspects.
The first is the mechanical completeness and accuracy necessary to a set of rules that is designed to allow simulation of life. The second aspect is the original or literary aspect. It is the implied world and setting that goes with the rules independent of genre. The last part of a rule book is genre. Rules can cover an amazing variety of imaginary worlds.