In the traditional sense of the word, "opera" refers to a work that is completely through-sung. That means no dialogue, no asides, and no verbal expression that hasn't been written to correspond to music. This is why Gilbert and Sullivan's works were "operettas" and why Les Mis can't be classified as a true opera.
The coining of the phrase "Rock Opera" played a big role in the distortion of the word's meaning. I think there are a number of works that legitimately exist as rock operas- shows like TOMMY and JCS fit well enough into the traditional meaning of "opera" (no spoken word, continuous orchestration) and actually do so through the rock genre.
At one point, someone must have taken a look at the rock operas of the time and decided that "opera" could also just be tacked on to a contemporary music piece as a way to proclaim/insist that the piece is profound and important. And wouldn't you rather be changing the world in a "Rock Opera" than in a "Rock Cabaret" full of "Rock Showtunes"?
So jump ahead to the days of RENT and now BARE. Both have been associated with some hip mutation of the word opera, and I agree that both are impressive creations with very unique, often groundbreaking relationships to the modern society. But IMHO, using the subtitle "A Pop Opera" was inappopriate for BARE and just beneath the level of the work itself. And RENT can't be a rock opera because it is not an opera nor is it rock music. It's mostly sung-through, so it is a musical theatre piece. The music is solid contemporary broadway material, dressed up as rock music through the orchestrations and voice styles used.
Both shows are substantial and want to be seen as substantial. Maybe instead of branding itself a Pop Opera, BARE should have just dropped the "Pop" thing altogether. Much the same way RENT should have downplayed the rock opera claim, splurged on a new sound design, and closed down for a season or two- put itself on "time out" until the producers learn why no other Pulitzer Prize-winning shows rely on their Teen People subscription for casting advice. But I digress.
So to answer the original question, sure BARE is an opera, and so is RENT and so is NAKED BOYS SINGING and the MARIJUANA-LOGUES and really anything else that considers itself too important to be a "musical".
"The last train out of any station will not be full of nice guys."
- Dr. Hunter S. Thompson
"I wash my face, then drink beer, then I weep.
Say a prayer and induce insincere self-abuse,
till I'm fast asleep"- In Trousers
