I liked it, but in a bid for authenticity the actors who played Muddy Waters, Howlin' Wolf and Little Walter—all key roles—affected thick southern sharecropper accents. I am so lilly white, so Ohio, so bloody Caucasian that I couldn't understand a word they were saying! What a bunch of mumbly sons-of-guns! Mrs. Wife turned on the subtitles for me and it was smooth sailing after that. This is all very embarrassing.
I noticed that Beyoncé, who played blues singing-junkie Etta James, was the only one who performed her songs from start to finish. All the other performers had song snippits. In clubs and studio scenes, they never seemed to sing to completion.
Then the credits rolled and I couldn't help noticing that Beyoncé was the Executive Producer.
It's her coin. She can do whatever she wants, I guess.