This book is a great reference for opera viewers.
What to expect from this book:
-Character names (helps you keep everybody straight in those operas with big casts)
-General background information (setting time and place, first performance date, who wrote the music and libretto, and the literature it is based when applicable)
-Some background information about the opera, its creation, its composer and/or librettist(s)
-Act-by-act synopses that help you follow or prepare for the plot
-Brief historical notes when applicable
-Some very light criticism of the score or libretto (I found this insightful and overall agreed with his comments
What NOT to expect from this book:
-Biographies of composers or librettists
-In depth analysis of theme, political or historical context
-Advice about which operas are worth your time and which to skip
-Reviews of peformances or singers
-Reviews of recordings
So basically, this is a good bare-bones book that will get you the information you need to understand the plots. Whether you just always wondered what Aida was about or you are preparing to see a production in person or on video, this guide will be a good addition to your experience. It seems like with 100 operas, you'd find every one you'd want to see and that is overall true but of the 50-odd operas I've seen, 14 were not in the book. (This is largely because what is in the standard reportoire is ever changing with society's tastes).
Even though this book was first copyrighted in 1957, the writing has not aged AT ALL surprisingly enough. I completely recommend this book.