The Victrola (Victor) Book of the Opera served two useful purposes in its lifetime. At a low price it allowed buyers of the new technology of gramophone records to read about the plots, histories, and music of popular operas. It also helped Victor record company promote their own discs of opera excerpts, at a time before Long Playing records when most discs could only include highlights. The book went through several popular editions in the first half of the 20th century.
So this book is out dated and had only one Opera by my personal favorite, Handel, but it's such a great reference to look at if you're someone like myself trying to discover new Opera's. Tons of great pictures and detail!
Charmingly nostalgic. The plot summaries and musical analyses herein are astute and still readable. At the same time, these books were in some ways sales catalogues, since they focused on the operas in Victor's collections, which were by necessity (in the pre-LP era) collections of highlights and excerpts rather than full operas. So the choice of content and the focus is not as useful here as many of the other popular opera summary books of the 20th century.