In art, when someone says a piece is "painterly," it means it isn't overly contrived. There is texture, and there are visible brushstrokes, and an organic, honest, and essential quality to the artist's work.
I think of David Sedaris' writing in the same way. There is such ease in his ridiculous, hyperbolic, raw, and ingeniously funny style. His words are spontaneous and lively. Sedaris' books aren't for the faint of heart, but they're worth every cringing, self-effacing, read-it-from-behind-your-fingers sentence. Painterly.