Flat UI is a natural progression from skeumorphism for the digital medium, but can only be boiled down so far.

With Apple's move away from skeumorphism to mostly flat UI and Android's existing flat UI, it's apparent that this will be the norm for some time. This UI aesthetic has a large amount of benefits.

I opted for textures in this site to contrast flat design.

While flat design aids usability and clarity while carrying its own associations with Modernistic and Swiss Design, it eventually reaches a point in which it is restrained in terms of expression. While skeumorphism attempts to be something it's not, there's still a great deal of genuine visual expression that can be gained in textures and other graphical affects. Visual effects do not need to be skeumorphic, they can utilize other design aesthetics that communicate and create additional visual hierarchy for the user.

"What’s the use of being legible, when nothing inspires you to take notice of it?" - Wolfgang Weingart

parallels with:

"What’s the use of being usable, when nothing inspires you to use it?"

While making sure our interfaces are usable is of the utmost importance, they do not exist in a vacuum. Flat design is still subject to overuse and being lost in the crowd of similar aesthetics. From a strictly information design standpoint, constricting palettes to solid opaque colors provides less options for visualizing complex data.

There's nothing wrong with the flat design aesthetic, it's just important to remember it's one of many strategies and can be mixed and matched based on design intentions.

Skeuomorphism’s Death Has Been Greatly Exaggerated also brings up an interesting point on the evolving definition of skeumorphism.

Let me know what you think @Aetherpoint