In terms of standard 17th thru 19th century repertoire, this is a comprehensive repertoire listing, which is particularly useful for teachers of advanced piano students to help choose pieces for students. A "difficulty" rating is assigned to every piece of piano music, which I would take with a grain of salt - this is certainly subjective. There are lots of nice unexpected surprises listed - works that I didn't know existed, and information on their publishers. In terms of modern repertoire, there are some helpful suggestions, but I think that the field is simply too big (as well as constantly changing as new composers come along), so pianists should investigate their contemporary music choices through other channels.