There's plenty of middle ground between the current extreme flatness and, say, MacOS X Tiger. An interface with a simple 3D bevel look (such as in Motif or the toolkit in NeXTStep) is no more skeuomorphic than than a flat interface, especially not considering how prevalent touchscreen controls are today.

Flatness to the current point of minimalism is, to me, very taxing and complex. Things blend together so much it's hard to tell where one UI element begins and another one ends. I frequently misclick in Windows 10/Office 365 even though I've used it for years now, simply because the flatness makes me misinterpret the layout and function of the UI.