My opera-singer reader Faith Puleston replied to my dig at the level of acting in opera as follows:
"There are acting singers and singing actors in opera. Some opera singers can't act at all (and often don't know it), while others, like me, love the dual challenge of being both actor and singer. It was reflected in reviews of my work. I'll look for some and post them to my website. These days much more is expected of opera singers than used to be the case, but I know that for me it was always of paramount importance to get under the skin of my character, sometimes at the expense of purity of vocal line etc. The problem is that there are moments in opera when it is impossible to gamble around and sing, when time stands still. Opera arias are more or less the equivalent of monologues in a play."
In my original post on this subject, I was kidding slightly, but I take Faith's point. There are and have been great dramatic actors and actresses in opera. Maria Callas was one great example - in fact her acting ability was admired enough by Pasolini that he cast her in a film as, I think, Medea. In contemporary opera, Nathalie Dessay has gone so far as to say that acting is at least as important as the singing in opera to her. But ultimately, I agree with Faith that a decent level of acting on the operatic stage is desirable, but when it comes down to it, it's about the singing, and you can't fake it when the moment arrives, the conductor cues you in, you fill your lungs with air, and you have to ride the wave of nerves and adrenalin to make those amazing lines of sound in the air, and, if the composer so wishes, to run from the highest note in your range to the lowest. As an illustration, here is Joan Sutherland singing 'O rendetemi la speme' from 'I Puritani', in possibly one of the greatest ever performances of one of the greatest ever arias: