In a better world, a film about Mavis Staples' journey from gospel singer through soul artist to living legend would have been made when she was in her prime.
In this routine, fitfully inspiring documentary, she's 76 - in one scene she returns to the Newport Folk Festival 50 years after appearing with her family's gospel group - and some of her present-day performances are a little over-egged.
As a retrospective, though, it's a tribute as richly deserved as the exclamation mark in that title. Staples' rich voice - she did baritone, contralto and blood curdling howl - was the major asset of the oddly named Staple Singers, who moved from Chicago churches to the recording studio in the early 1950s.
Those who remember Mavis' spine-tingling reading of a verse of The Weight in The Last Waltz, will also recall who sang next: Roebuck "Pops" Staples, the paterfamilias, who died in 2000, was the group's founder and his steady gentle presence rightly saturates the film.
