Since I didn't see her and DO lament the fact, I can't speak about her stage manner. She was very heavy, but also had a very expressive and not homely face. The Carnegie performance to which Bob refers was very highly praised by friends who were there, and they talked at lenght about the "aliveness" (that's not a word) of her tone and the beauty of her phrasing.
The evidence, IMO, is overwhelming that she was a quite phenomenal singer for about a dozen or so years. The RAI Vespri Siciliani is on a level with that of Callas from Florence. Yup, I said that! The Forza on RAI, while a little driven, is about as grand as you will ever want to hear, the Norma from Rome (the famous Callas walkout replacement) is almost perfection, a little carping from me in the soft passages, and the first cabaletta could have been more cleanly sung. Etc, etc. The aria "O Re dei Cieli" from Agnese di Hohenstaufen, both on the RAI recital and the London (Decca) recording are perfection. There is no other word. I can think of no singer in the post war era, and mighty few before it,who could have done with that music that which she did.
What'd I forget. Ernani on RAI is a knockout, Aida from Mexico, ditto. True, the very top could sometimes be driven, but she always found the note, and ascents to them and descents from them were always cleanly articulated and in time. No faking from her.
Yes, I do very much regret having heard what to me is one of the most imposing, equalized and beautiful sounds ever to be heard on recordings. I cannot imagine the live persona to have been that much different.
P.S. Gioconda on Decca is not her greatest event. And yes, Norma was begun and never completed. The cast was to have included Simionato and del Monaco. No documentation that I know of has ever been forthcoming as to the reason. The two great soprano mezzo duets were recorded and are somehwere in Decca's vaults. Perhaps they could give us a clue.