If you check out Inside the Labyrinth, which is a behind the scenes documentary about the Jim Henson film with Jennifer Connolly and David Bowie, you may not get anything too special as far as the quality of the direction of it. It shows you talking heads and it doesn't go into any of the real nitty gritty of things that happened behind the scenes (for example, Terry Jones was one of about ten writers on the film, and Jones happened to get the final screen credit, and Connolly was one of many possible actresses for the lead).
But the reason why it is something of a must see is simply because you get to see Jim Henson talk about and show what the process was to create so many of the delightful Muppet effects - the animatronics in large part, but the great variety of approaches, from the mouth-puppeting (thanks to Terry Jones's idea in the script) to the largest puppet that the Henson company created at over 15 feet tall - and how his performers pulled it off. It took a lot of trial and error at times to make Labyrinth, and however you feel about the movie, classic or folly (some critics panned it upon original release), it has so much innovation that it builds upon the already wonderful stretches into puppeteering that the Dark Crystal made (also collaborated and designed with Henson by Brian Fraud).
So no matter how standard the presentation might be, it's the substance of it, how every decision got made, what you see with the rehearsals of the performers, how a dance sequence is put together, how computer effects and carefully choreographed black-suited actors, etc etc, gets pulled off, that makes this so essential viewing. Hell, you even see David Bowie recording one of his songs and acting opposite a baby (and that baby is one of the few things to cause Henson a headache here)! It made me respect the movie more.
