For fans of Callas, this is about as good as it gets, and you must have it in your library. The interviews with her, taken out of the context of the whole, make this documentary worth having. Insecurities and other emotional baggage notwithstanding, Callas knew who Callas was. She provides an excellent perspective of her place in the art of music and opera specifically. Her views on art are a revelation.
For fans of opera, but not necessarily Callas--And, yes, she is an acquired taste!--the documentary is instructive on a revolutionary period in the history of opera. The documentary earns its place as an historical document.
Callas was a teacher on many levels. Her inspired mentoring of Caballe, for example, contributed much to the body of art we have today. Without Callas, we may not have had the magnificence of Caballe's "Norma". I only wish there was footage of Callas's master classes. I wish I knew something about the singers she coached, and where they are today.
Zeffirelli's narrative, handling of the contributing artists. and smooth transitions among archival footage and interviews are especially fine. Zeffirelli, himself, understates, rather than overstates his case. One has the sense that one is seeing and hearing the truth. Caballe's thankful tribute, however brief, was lovely. Gobbi's anecdotal comments will bring an iceberg to tears. Gobbi, all by himself, provided such an insight into Callas's inner being.
Enough! Read the other reviews! Then, buy it!