(2) Opera is a dramatic art. Never mind Kerman; I mean the energy released and channeled, between all participants, by placing performers among each other and before an audience. (Aristotle was an early commenter on this phenomenon.) Some performers are attuned to these currents and can conjure marvels; others less so. Ditto directors, and librettists, and of course composers.
(3) Opera illuminates the world, and one's experience in it. Ours, or one comparable -- in the smaller touches and broader. On this hook come the ridiculous contortions of "Regietheater", but fortunately that hasn't taken much hold here. We learn from how a performance shows the world, or wallow in it, or find it poorly-done, or just intolerable. (A friend finds the character Otello too blockheaded to be convincing, or sympathetic. I find Khovanschina shockingly close to an apology for Wahabbi theocracy.)
(4) Opera illuminates its own world: the history, present, and future of opera. Every performance revises all of these, to our delight or chagrin. A new work may be revealed, another incrementally forgotten. For those who keep track, an unexpectedly impressive debut may redeem a dull evening, or a favorite's missteps ruin otherwise great enjoyment. For friends or colleages especially. And even those far from "inside" are part of the history too, having been at that earlier performance when it was, you know, a Golden Age of this or that...
(5) Operagoing is a social activity, beyond and around the sitting-in-the-dark-as-an-audience part. This, oddly enough, may be the only definite idea most people have about opera. Still significant, though.
Now it seems to me that not only do we experience an opera performance through each of these lenses, but all of us have personal (that is, differing) tastes and priority-weightings as to every one. So one of us might find the most significant sense-element of a production to be singing, while another responds most strongly to handsome sets, and another to the sound of the orchestra. At the same time one might be most interested in the sensual aspects, while another seeks out the strongest dramatic experiences (by his lights, naturally) and barely registers direct sense impressions, and so on.
One problem is that a strong impression as to one of the aspects -- especially one of particular interest to the operagoer -- can make it hard to admit or even see the truth as to another. I've pointed to one example of this.
Another problem is that that current writing doesn't cover all of these aspects terribly well. But more in another post.