While I am thoroughly interested in Wittgenstein's theory, I am perhaps more interested in the stylistic transformation that took place between the Tractatus and Philosophical Investigations. The Tractatus, in form and content, seems written without an audience in mind, or at least without a questioning, doubtful, human audience, anyway. Philosophical Investigations, on the other hand, anticipates skepticism, and at times even calls out directly to the reader. I first became conscious of this on 152, where he writes: "Do the others, perhaps, hover before one's mind? All of them? And while one is saying the one sentence, or before, or afterwards? --No. Even if such an explanations rather tempts us, we need only think for a moment of what actually happens in order to see we are going astray here." First of all, I love the emphatic "No" he frequently uses. (I love it the most at the bottom of 163: "Can you give the boundary? No." It's as if he's saying, "No, you can't, so why don't you just listen to me." I cannot recall any such feeling in the Tractatus-- there was instead an implicit feeling of "if you don't understand, I don't care.") Secondly, he recognizes and anticipates where the minds of his audience might stray and preemptively guards against this straying, exhibiting a consciousness of audience that prevails, ultimately contributing to this text's (vs. Tracty's) readability.
Other moments: pg. 157-- "Do not say: 'There isn't a last definition...'"; pg. 163-- "... don't think, but look!"; and the very fascinating moment when he writes of "the author of the Tractatus Logico--Philosophicus," effectively putting even the past version of himself into his intended audience.