A cultural artifact is well designed if it approximates some deeper nondual within the western worldview. The nonduals in the western worldview are Order, Right, Good, Fate, Source, and Root. See http://nondual.net Thus we can think of something being well designed at each of these levels. So for instance a designed thing might be well ordered in its design. But well ordered does not make the design right, getting the design right is a completely different issue that well ordered organization of the cultural object. But having things right does not always mean that the design is good. We can think of the difference between order and right as the difference between the law and the spirit of the law. But a law being good has to do with whether it supports variety of life, goodness has to do with variety generation rather than selection of one design over another as the term right suggests. So a design that adds to the variety of some cultural artifact may be good without being selected as being right. The next level is fated design. For instance our own design is fated, we cannot change our physical organism fundamentally and live even though we can make all sorts of modifications. Fated designs are channeled into a particular solution set by some sorts of external factors that are out of the control of the designer. Source design has to do with what Plato calls the source forms. The sources are the projected schemas or templates by which we design things which we cannot avoid. Root design has to do with there being a single cause for all design as it wells up in existence. Design activity is human activity, and in some way it is what makes us human and differentiates us from Neanderthals for instance who did not change their material culture in innovative ways as humans did starting about 35000 years or so ago. Neanderthals and Humans shared the same material stone age culture up to about that time. At least that is what I remember from the books I read on Neanderthals. But of course we now know that there were different species of Neanderthals and not just one. The point is that there is something about humans that crave innovation in design, and want novel emergent properties in cultural artifacts. So design is part of what generates the Emergent events in human cultural change and the development of arts, crafts and technologies that support our existence in our lifeworld. Alexander talks about a Quality with no name. This is one way to talk about the nondual approximation of what is well designed. However, we know it when we see it, or at least we pretend to.
Quora answer: What makes something well designed?