What factors make for a great statistics book? In other words, what writing styles, visualizations, explanatory methodologies, text length(!), tone, depth, etc, etc contribute to giving the audience a great education, understanding, or perhaps even entertainment? The question could perhaps also be framed as "What advice would you give to someone writing a stats book?"
I'm not looking for any specific books, but of course, example are welcome if they epitomise a particular quality. Factors that apply to texts other than books are also welcome.