Scholars and critics say that Herr Wagner's talent was in synthesis. The negative critics, e.g., specialists in a field from which they feel Wagner has stolen, tend to discredit Wagner for that. The grail was not, alas, the cup used at the last supper, prior to the opera "Parsifal" anyway. What's more the Grail theme was plagiarized from Mendelssohn. The plot of the Ring was not, alas, the same plot as the German novel "The Nibelungenlied." Wagnerians like myself, rather, see that synthesis as a symptom of Wagner's genius. He was able to take a series of sources, stories, novels, epics, songs, and cement them into a supreme art form, Gesamptkunstwerk, better than the sum of all the parts.
Newman comments intellegently on all aspects of the operas. He includes musical themes--surely a necessity in the work of that expert user of the leitmotif!--and even the psychological dimensions of the music. (Before I saw "Tristan und Isolde," I attended a presentation of a musicologist who nearly broke into tears as to the depth of the music in that opera. His comments reminded me of those of Newman regarding the same piece, which reminds me of Jung, one, whom you might say, was a product of some of the same Germanic trends of the late 19th century. But, enough on that...)
I read each review before I see the opera to which it applies. I read them again periodically. They are magnificent, allow for reasonable criticism. But they also give the devil his due.
I cannot recommend the book more strongly for anyone interested in Wagner, especially if you plan to hear or see the operas. Then leave the volume next to your bed. It's well worth re-reading, learning all dimensions of the music of perhaps the best composer who ever lived.
Is that extreme? Perhaps. Was Wagner's genius extreme? Off the scale.
Read and enjoy it.