Summary: Flat Design Origins reveal its strengths and weaknesses. Flat Design comes with negatives and positives. It's main challenge is "correctly" implementing Flat standards that work for your UI or brand .
Summary: Google's Material Design language reinforces one of the most valuable principles of graphic design and user experience: provide design elements that make it clear that a control is present for use. This technique is called a "signifier": it signifies how to interact with the UI.
Visual designers, Creative Directors and UX designers have been on a mission for the past five years to "clean up" or minimalize UI design. The approach is called Flat Design. Design minimalism is not new and the intentions of de-cluttering your design are vital. However, industry studies and our own usability tests conducted on Web, Web App and Mobile apps tell us that there are a few things missing from most approaches to Flat design or new hybrids like "Flat 2.0".
The graphical or visual aspects of an interface are the most easily recognizable. They require no methodology (Graphic design vs usability) or design distinctions, (What is design?).
Everyone from CEO to programmer can understand an interface by it's visual treatment. For some the interface is "eye-candy" and for others representative of organized emotional response and visual perception.
Oftentimes, the confusion over who dictates the design can lead to confusion and often a gratuitous use of graphics. This problem can be compounded by an interface being dictated entirely by a designer (where usability resources are absent, underfunded or ignored entirely from a development process).