What is opera?

The quality common to all the great operatic roles, e.g., Don Giovanni, Norma, Lucia, Tristan, Isolde, Brunnhilde, is that each of them is a passionate and willful state of being.  In reali life they would all be bores, even Don Giovanni.

In recompense for this lack of psychological complexity, however, music can do what words cannot, present the immediate and simultaneous relation of these states to each other.  The crowning glory of opera is the big ensemble.

That is from an excellent W.H. Auden essay “Notes on Music and Opera.”