No rating for this: it's one star and five star at the same time.
What is maddening in Adorno, is that his remarks are always to the detail and often ingenious, yet they are set inside a structure that is not only "fragmentary" or "paratactictal", but next to unfair to any reader who is not dedicated to sit through 150 pages of difficult prose, that can change the topic whenever. I recommend starting to read at chapter 7. Here Adorno takes up the historical and political conjuncture of Gesamtkunstwerk and the commodification of arts in the latter part of 19th century. First and second chapter are far more difficult and hermetic.
Readers of Adorno know that he seldom works out transparent narrative or conceptual gridwork, but also that he has a frustrating habit of not opening up his "anti-system" for rigorous criticism. Here that tendency is quite exaggerated. Especially, Adorno leaves out many theoretical and historical building blocks, and concentrates on rhapsodies and variations, that go on for unlimited length, leaving the reader in the dark about how to read and balance out his many allusions to philosophical figures, such as Marx, Nietzsche, Freud.
Yet, this being said, Adorno's view on Wagner is substantial. Commodification and differentiation of arts is for Wagner the problem facing stage art and music - and Adorno totally agrees. Adorno clearly sees the progressive element in Wagner. But, according to Adorno, Wagner's solution is proto-Fascist as he sets together by ingenius fiat something that could only be presented truthfully in constructivist manner and with planned collective work. Adorno's take on how cinema is structurally based on some of the technical breakthroughs of Gesamtkunstwerk are wonderful.
The question of anti-semitism as integral part of discussion. Adorno doesn't oversimplify matters, for he sees in Wagner a musical modernist, who paves way to Schoenberg and Viennese atonal school. But for him, Wagner is essentially and philosophically anti-Semitic, and he would not have agreed with the suggestive question, prefacing his book: "Why is Wagner worth saving?" (by Slavoj Zizek and Verso). Make no mistake, Adorno's task is ruthless critique, not "saving" Wagner. This is best part in Adorno for those of us, who feel that capitalism has betrayed the majority of people. Adorno does not suggest that we should cherish or "save" the historical roots of this betrayal in arts and culture, but expose them as what they are.
The chapters finished for the 1952 first complete publication by Suhrkamp (Chpts 3,4,5,6,7,8) are more balanced, and in fact more informative. Yet the chapters already published in the Zeitschrift für Sozialforshung in the late 1930s (Chpts 1,2, 9, 10) have the most weighty judgments about what role Wagner plays in the "spatialisation" of music in modernity. Anyhow, reading them last is the route I suggest.
I recommend the book if you are interested in commodification of music and history of art and capitalism, and if you can stomach Adorno's style. Myself, I think Adorno's argument, if not essentially "right" all the way, poses the right questions, and this is what matters. Also, I think this might be THE best place to start, if you feel that something goes crucially wrong in Walter Benjamin's account of how the mechanisation of arts leads to general revolutionising of social relations, argued for in "The Work of Art" -essay. It is a pity Adorno's presentation borders on arrogant, but if you get past that, there's lot to salvage.