One aspect of Newman's books about Wagner that's not often mentioned is the quality of his prose style. He's an excellent writer, not only in the book under review but even more significantly in his 4 volume biography of Der Meister, which makes its daunting length (apprx. 3,000 pages) seem irrelevant. I don't want to exaggerate but reading Newman's magnum opus is a lot like reading Gibbon's Decline and Fall. Gibbon is a greater writer, no question, but Newman certainly knows how to push words around on the page to pleasing effect.
Newman's comparison of Wagner's operas with Strauss's tone poems, the coda to WAGNER AS MAN AND ARTIST, is one of the most interesting parts of the book, though I doubt anyone would think EIN HELDENLEBEN or Salome's final scene is worth as much attention as Wagner's music, including Strauss himself.
Newman's major blind spot in his writing about Wagner is not anything about the subject, but his wrong-headed reading of Nietzsche. Newman claims he had enough material to write a book about Nietzsche, and, if I remember correctly, was approached about doing so, but I for one am glad he didn't write it. He seriously misunderstands Nietzsche's philosophy as well as, in my opinion, the significance of his relationship with Wagner and Cosima.
But his monumental biography, as well as the book under review, are absolutely essential reading for anyone interested in Wagner, in spite of one of them now being over a century old (WAGNER AS MAN AND ARTIST--1914; THE LIFE OF RICHARD WAGNER--volume 4 published in 1946).