“Many passersby react to the opera with a momentary perplexity that seems to fade as they walk on. Others become curious and ask questions. By the end of the run, thousands of Angelenos will have joined the piece’s accidental audience, which may turn out to be the more important one. Whatever the reaction, “Hopscotch” triumphantly escapes the genteel, fenced-off zone where opera is supposed to reside.”