I saw this documentary on The Simpsons Season 1 DVD set.
While Simpsons maniacs will be disappointed as this documentary basically answers general questions(e.g. Where'd Matt get the idea for the characters? What does Matt do other than The Simpsons? You know, stuff they know by heart by now), it pleases anyone who had a question about the series. Just don't suspect they'd go into detail about single episodes. Definitely doing it's homework, it does get out the info through interviews with people you'd expect, if slightly short.