Recently I was privileged to hear a young composer do something entirely unplanned, i.e., entirely instinctual, with a Bach Two-Part Invention: He played it as if out of his own sense of line and rhythm. It was like listening to Arvo Part's transformation of the F minor slow movement of Mozart's early F-major Piano Sonata. It was at the same time entirely Bach, entirely this young man's, entirely adult, and entirely fascinating.
Interesting that the word "entire" keeps turning up here. That is what it felt like. What more does anyone want out of music?