An essential classic I can finally say I've seen, and Frederick Wiseman's worst nightmare.
It's fascinating in its own right, but also amazing how influential you can argue it is. You could trace the origins of many Adult Swim and similar type shows/humor back to Grey Gardens. What came before this?
And while it may not be on the same level as Salesman (not many films are), it's still great. In Transit is the only other Maysles film I've seen, but it is now that much clearer that I need to see more.