I don't get the blanket hate for skeuomorphic GUI design, because good or bad design can be either flat
or mimetic.
The primary function of a GUI is
affordance, meaning: it should indicate to the user what the element actually does, through its form.
In the case of Apple's various ridiculed "desk-diary" app stylings the mimicry employed made no sense at all, because their apps were often so simple that the woodgrain effects served no real function. In those apps the textures and shadows did not indicate a function but merely provided dubious decoration. But that ridicule then triggered a blanket assumption that
no application could ever have affordances improved by indications of depth, shadow, a groove,etc. I think this is incorrect, because it is well know that humans target aquire much better on elements with pseudo-depth, and pattern recogition of elements is improved where items conform to expectations.
Of course - It's possible to use flat design to indicate functional segmentation, but what is the aim of this? Surely providing Simplicity and speed in target acquisition! "I need the filter cut-off, aha, there it is!" . Fast.
When a designer employs the flat style they must include new ways to say 'this is the filter' and 'this is the cutoff', perhaps specific colouration is used, or perhaps the labels are more explicit "filter cutoff". There are trade-offs, and these trade-off often mean something is lost.
While it is fully possible to deliver a flat, simple, interface to demonstrate segmentation of function - quite often these designs fail when the interface is hard to understand, elements look too similar, elements are hard to find, elements are hard to determine the function of, elements are hard to separate.
I consider it totally fine to have a 'knob' with an indication of depth, and a pulldown menu without depth because I'm not being suckered into some fantasy that I'm looking at a
physical Moog here, I am only using the pseudo-depth as an indication of the graphic element's usage.
