Schopenhauer stands out as one of the most gifted writers in the history of philosophy. This book is long, but every paragraph is packed with insight. The only time he ever gets long-winded is when he is tearing into something or somebody that bothers him. Other than that, the book offers a profoundly pessimistic, insightful, witty, and sophisticated worldview that has influenced me profoundly.
Volume two is a commentary that he wrote years later to flesh out the ideas developed in the first volume, and is every bit as insightful. We only have so much time to read, however, and volume one is a consistent whole. I do not recommend Safranski's biography, however, because it is incredibly melodramatic and wordy. I couldn't finish it.
I believe that most people would find Schopenhauer's worldview to be paralyzing and unbearable; however, if you have a melancholy or brooding temperament, you will feel as if you have finally come home after all those years of disillusionment. As Schopenhauer frankly puts it: aging is a process of exchanging hope for insight.