Lightning in a Bottle
I always like a good concert film. The style of music doesn't really matter as long as it is performed well and the people doing it look like they are having a great time. I don't really know that much about Blues music, but as one of the participants said, this movie is like they "looked in the phonebook under Blues and invited everyone they could find."
Even though they were only short clips, some of the behind the scenes footage and archive performances were great. My favourite was the footage of Jimmy Hendrix watching Buddy Guy doing his thing.
Of the performances one my favourites where Ruth Brown, Mavis Staples and Natalie Cole serenading Bill Cosby. The other stand out songs where Angelique Kidjo singing Voodoo Child with Buddy Guy on guitar and BB King's final numbers.
Some of the choices for performers are cause for debate though - Steven Tyler?
I would recommend getting this on DVD if you are into Blues music as there were some bands that were not shown (such as Jon Spencer Blues Explosion.) You also get the bonus of being able to skip the performers you don't like.