There's some overexuberence in it. I, for one, did not spend any time playing about with sentences purely as forms, without interest in content, but I managed to learn to write.
And it does tend to concentrate on those gem-like quotable sentences that can't really make up the bulk of your writing. (Though it does make easier reading. I've noticed that most sentences, regardless of style, tend to sound dorky in isolation as examples of How To Write. He doesn't cite any of those.)
But he does have useful comments about sentence structure, and the observation that there is really only one grammar error, namely not having your words properly related to each other. On hypotaxis and parataxis, which he not unnaturally calls the "subordinating style" and the "additive style" while describing the uses (and dangers) of both a complex system of subordinate clauses to carefully structure words together, and the airy stringing of things with adds and other conjunctions.
He allows the return of meaning in discussing satire, and then first sentences with all their need to draw in and foreshadow, and last sentences with all their need to sum up, and how stupid, banal, or pointless they often sound in isolation. (Doesn't go into middle sentences, which are far more interrelated with other sentences.)