Oliver Reichenstein, in an interview with The Verge:
Good screen design happens in the subatomic level of microtypography (the exact definition of a typeface), the invisible grid of macrotypography (how the typeface is used), and the invisible world of interaction design and information architecture. Minimum input, maximum output, with minimal conscious thought is what screen designers focus on.
Update: Some of you responded on Twitter saying good design isn’t always invisible. Case in point: my letterpress posters (if they can be considered “good”) employ design that is very visible.