GNOME and the GIGO Principle
GNOME 3 is usually defended in terms of design excellence. However, while GNOME has been developed with close attention to design, that does not mean that its basic foundations are as grounded in design principles as you might infer.
Rather, a look at GNOME 3's early history shows that development was mostly a consistent realization of principles described early in the process -- principles founded on the impressions of the Design Team and apparently backed by little theory. This inconsistency between how GNOME is marketed and how it was actually designed seems the major reason for its sometimes rocky reception.
This is not the story GNOME tries to tell. Instead, GNOME 3 is described in language that implies a triumph of design. On its home page, GNOME 3 is described as "designed from the ground up to help you have the best possible computing experience" with words like "crafted" and "harmonious whole" added for good measure. The GNOME Shell design page has a similar emphasis, with the design expertise of the project participants mentioned in the first paragraph.