My interest has been sharpened recently by reading Owen Toller's book and listening to the Berlin Classics set reviewed on this site. Toller's exhaustive book digs deep into the music and the biographical context with points spanning the two interacting domains. I cannot pretend that this chapter makes enthralling reading but the problem is the subject not Toller's exploration. Clearly much thought and love have been channelled into the pages of this book. Rewards for the reader are commensurate.
Negative observations are only twofold.
Secondly the highly detailed tracking of the opera and plot is presented with landmarks by reference ONLY to the score. Do not misunderstand. The text reads coherently by itself. How much more valuable this book would have been had it been keyed into the DG discs with episodes and moments shown by reference also to timing readings within tracks. There should also have been a list of recordings both private and commercial.