Opera combines virtuosic singing with music, drama, and spectacle in the same way as ballet combines virtuosic dancing with music, drama, and spectacle. They are both considered esoteric forms because they require an enormous amount of money to produce and an infinite amount of work to attain even a minimal level of performance.
They are not esoteric in so far as being hard to understand. I introduced opera to my children by sitting with them, when they were each five years old, and watching Ingmar Bergman's film version of Mozart's "Magic Flute," which is basically a fairy tale. I told them the story as we went along, and that seemed enough for them to then watch it on their own, about five hundred times....along with other favorites like Betty Boop, Snow White, Pinocchio, etc., which they also watched five hundred times. This is impressive inasmuch as the opera is three hours long, perhaps two and a half in Bergman. But they didn't know they weren't supposed to like it or that it was too hard to understand, so they just watched it over and over and over again. (It has english subtitles.)
Ideally, you should go see an opera and, like everybody says, they do have supertitles, which makes it easy to understand the plot and dialog. But opera, like ballet, is produced as HIGH ART and therefore takes place in a fairly sterile atmosphere enabled by huge sticks stuck up everybody's asses -- audience and performers alike. In my whole life I have seen exactly two good productions of an opera; it was "Marriage of Figaro" both times, once in London and once in L.A.
As I see it, there are two kinds of opera: the first is spectacle + virtuosic singing + beautiful music, which you can find in Gluck, Verdi, Puccini, Donizetti, etc.; the second is an ineffable other world, which you can find in Mozart and Wagner. It's not that one is bad and the other is good; they're just different and have different things to offer. So, as an example of the first, before you die, you should listen to Maria Callas singing "Casta Diva" -- You Tube has it
http://www.youtube.com/watch?v=MBW5a77wINQ
but the sound quality leaves a lot to be desired, so you might check your local library to see if they have a copy. Or listen to her sing anything by Verdi.
As an example of the second, you should give Bergman's movie a try. Netflix has it. I think it's one of his best movies.
If you like that, you should try "Marriage of Figaro," and if you like that, "Don Giovanni." Peter Sellars has a very interesting filmed version of Don Giovanni, set in modern day Bronx.
Doug can enlighten you about Wagner. I don't know nothing about that. And Michael Pollak is probably the man to articulate why Mozart and Wagner are in a category of their own. So far as live opera is concerned, you might have better luck with amateur productions than with New York Met type stuff if you want to figure out why anybody cares about this shit.
Joanna