So far, hip-hop theater’s most distinctive, exciting quality is ‘how’ — the way in which its stories are told. In the brightest moments of ‘Flow,’ Will Power shows that hip-hop’s fusion of verse and song could make it a potent update of the traditional ‘Oklahoma!’-style musical, one better suited to the stage than rock music. Like Rodgers and Hammerstein, who proved that even a carnival barker can sing a musical soliloquy, his work suggests that hip-hop’s narrative tools will function well beyond one generation’s concerns.” Maybe hiphop musicals operate more like opera, “with one critical exception. ‘Right now there are no conventions, the way opera is full of well-understood, time-honored conventions. It’s evolving now.”