I've also heard that it doesn't show Prost in a very good light, but I'll choose to ignore that element as I know it not to be true.
Films and footage are fantastic but you can't tell the full picture in 90mins of screen time, for the casual fan then I'm sure it's a fantastic documentary, for those wishing to learn more about Senna and that period then it will be equally enjoyable but I would urge people to balance it by reading the numerous books available.
I still can't wait to see it