Stephen Sondheim launched a theatrical tempest by complaining in advance about this "reworking" of the revered but rarely staged Gershwin-Heyward opera, which opened at Boston's American Repertory Theater prior to a Broadway run scheduled for January 2012. Actually, it's a triumph. Director Diane Paulus and playwright Suzan-Lori Parks have tinkered with the book, though not terribly, and tailored the show for a Broadway stage, not an opera house. The story of a crippled beggar and the "loose woman" he loves comes through as strongly as ever, and so does Gershwin's incomparable score, beautifully sung by a fine cast headed by Audra McDonald.