How is this book not talked about more often? It's the most ingenious and effective method I have found of acquiring a language (even better than the famed Familia Romana, in my estimation).
The mechanism is simple and elegant: a grammatical concept is explained, followed by a page or two of sentence examples. What makes this amazing is that you first read the French, then turn leftwards to compare your translation to the author's. After a couple of sections like this, the chapter ends with a text or two that use the example sentences (the texts are always real extracts).
This method has the effect of rendering to the reader confidence that his understanding of the text is exact. Likewise, it's immensely satisfying - you start a chapter not knowing how to read the end text and later breeze through it with relative ease.
The end result is that one has read the likes of Pascal, Tocqueville, Bergson, Baudelaire, Voltaire, etc.