Purists or anyone allergic to experimental-theater tropes (metatheatrical gags, presentational acting, deadpan delivery) may flee at intermission. At my performance, a few did. It helps to read the original libretto or watch the 1936 film before going. I did both, which help me appreciate how the staging scraped away a century of cultural rust and sentimentality to reveal an often deeply sad and frequently funny masterpiece of music-theater. Full disclosure: It was the first Show Boat I ever saw live. Will it be my last? Centenary’s coming in two years. Will the country have moved on so much that no rewrite would justify a return to Broadway? Or will Ol’ Man River roll backwards, sweeping us into a past where we don’t belong and don’t want to live?