I rather enjoyed it.

There are a lot of people on here that seem to be disappointed by this film, but I enjoyed it for the most part.
Getting to see David working and just hanging out was all I expected from it, so I guess if you expected more I can see why you'd be disappointed.
I loved the footage of David giving cryptic direction to Laura and the girl in Poland while working on IE. I loved the phone conversation between him and Jeremy Irons when he was trying to tell him about his part, just trying to imagine what Jeremy must be thinking and saying. I loved seeing him work on a painting and shooting photos in factories in Poland. I loved the brief scene of David trying to find the right sound for the vocals for that song in IE, though I wish they'd shown more of the recording process. The only parts I didn't care for that much were the scenes of David telling stories about being in Philadelphia. I'm sure in real life I could listen to him tell stories for hours, but it didn't really translate to interesting film.
So, yeah, overall I thought it was an interesting, unprecedented look at the creative process of a modern day genius.
If you go into it expecting some sort of insight into what his films mean or why he does the things he does, you probably will be disappointed, but considering he's never talked about such things and probably never will, you should know that going in.