Reading this online is very challenging. Well, reading any text online is challenging. Williams' writing, however, is very clear. Though originally written as separate essays, each chapter builds on the last smoothly. The chapters ultimately form a cohesive picture of Wittgenstein's later work (an immense achievement in itself) and a thoroughly engaging criticism of Cartesian thought.
Just a few highlights (though I think this will take far more time to complete)
Chapter 3: Wittgenstein and Kant: On the Metaphysics of Experience, Williams does a better job illuminating Kant than a few books on Kant alone have done. One of my favorite quotes from this book is in Chapter 3 as well, "Wittgenstein [as opposed to Kant, takes the approach of:] mapping out the contours of particular areas of discourse."
And this:
"Wittgenstein seeks to convince us that there is no underlying structure or order of language and knowledge that informs and warrants our ways of talking. There are only our ways of talking."
Williams' talent for thorough yet lucid and engaging writing is such a gift to readers - even those with limited exposure to the many authors to whom she references.