Robert Mugge’s video about the Delta blues singer, whose life has long been shrouded in myth, includes some fascinating interviews with people who actually knew Johnson. But Mugge uses other musicians to perform Johnson’s songs, and while some of their renditions are good in themselves, they’re far more conventional in their rhythm and melody than Johnson’s extraordinary recordings, in which his singing can almost become speaking. Thus a truly original talent is reduced to a mainstream entertainer whose spirit can be captured by the likes of Sonny Landreth. In a similar fashion, Mugge places some scenes in the glitzy interior of the Rock and Roll Hall of Fame and Museum; it seems a world apart from the jim crow south where Johnson made his music, though Mugge misses the irony.