Dialogue with Heidegger: Greek Philosophy Book

As a book of history, the author is no doubt correct, but as a work of philosophy, this book is a complete disaster. At no point does the author ever clarify or explain a thinker's position, he only states it. E.g., "Hegel was an idealist" would be a correct claim found in this book, but what that means or entails is never forthcoming. Every time the author introduces a new theorist, although he states the beliefs of the theorist, he never provides the justification for those beliefs, thus this is a terrible philosophy book, despite being a correct and useful history book.