Documentary makers are NOT artists. The worst kind of documentary maker is the kind who thinks he's an artist, and I suspect that the worst kind of "artistic" documentary maker is the kind who began as a painter (or some such). In painting, aesthetic considerations really are paramount as they are almost nowhere else. Painting is an art form with no social influence whatever, and a painter's ONLY professional obligation is to create beautiful pictures. A documentary maker, unlike a painter, has several potentially conflicting professional obligations; chief among them (listen carefully, Greenaway) IS TO INFORM.
A couple of times Greenaway's film threatens to be informative - as I recall, there's a brief discussion of what happens when a body is struck by lightning, and an even briefer synopsis of the physics. But Greenaway undercuts both moments by letting us know he's an artist. Running across the bottom of the screen, to make it as easy as possible for us to avoid actually learning anything, is something like the following: "Lightning effects are called for in Macbeth, Peer Gynt, The Tempest, King Lear..." I don't want to be given a list of stage works involving lightning; if I wanted such a list, I would compile it myself, which would be fun. On the other hand, how lightning is conducted through a human body is exactly the kind of thing I do want to be told - and which images would help me understand. My eyes drifted to that damned pointless list for a moment, and I missed it.
Greenaway's works of fiction may well be brilliant. Michael Powell, possibly the finest director Britain has ever produced, wasn't any good at documentaries, either. He only made one, at the end of his career, when he couldn't find anything else to do. Watching it you sense exactly the same thing as you sense while watching "Act of God": an artist - whether good or bad, it's impossible to tell - utterly ill at ease, doing what artists were never meant to do, and not knowing how to go about it.
And what's with Greenaway's technique with his interview subjects? He cuts away from them in mid anecdote, sometimes mid SENTENCE, for no reason except to make them look foolish. If they came to him in good faith, he had no right.