I saw it at The Belcourt last night, and really enjoyed it. The documentary focuses on Stefan Knüpfer, but to call him a "piano tuner" is like saying Walt Kelly "liked to draw funny animals". Knüpfer is the chief technician for Steinway in Vienna, and the film follows him as he prepares various pianos for the specialized needs of several top rank pianists.
I came away feeling that Knüpfer, in his vocation, was just as worthy of being called "genius" and "artist" as any of the pianists he labored to please. And it made me really question any distinction that might be drawn between "artists" and "craftsmen". Like vocal categories (bass, baritone, tenor, etc.), such labels are helpful for classifying people (and thus limiting them), but are in truth arbitrary distinctions that don't really exist. I think Knüpfer is an artist, pure and simple.
It was also reassuring to see the level of obsessiveness with which he and the pianists regarded the finest shadings of sound and tuning. And was I kidding myself when I began to feel that I could sense the differences, if not exactly "hear" them? Helpful to remember that the little details we obsess over do make a difference in the final work! As Stephen Sondheim was not the first to say, "God is in the details".