It was an incredibly interesting film, told in a sort of essay style with Greenway's own floating head narrating. I'm still amazed by the opening sequence, which you can see here (and also get an idea of what I mean by floating head).
Through this investigation Greenway argues that people today are visually illiterate. The layers of information included in something like Nightwatch is lost on the average viewer. It's an interesting concept, especially considering the shear volume of images we are bombarded by everyday - which is a likely cause of our illiteracy. Of course, not all (hardly any) of the images we see daily are going to have the depth of a Rembrandt painting, and having the time and resources to fully explore the context, history and motivation behind the painting is an incredible asset (luxury). But I've personally stood in front of hundreds, if not thousands, of images and only taken a cursory glance.
I need to read (the image) more.