Uhh... The Metro, "intuitive"? Are you smoking crack? Clean it is, after all is difficult to be more "clean" than a plain pastel-colored rectangle with some text. "Aesthetically pleasing"? Bah, just look for a few seconds to realize that the real reason is laziness/lack of time to do something more elaborate than pure rectangles with some text (good UI elements are a art and good art is HARD).
Trust me, when I make a button using "flat elements" is because I have no time to make a more elaborate button that is appropriately represented in several resolutions and can be resized, I'm deliberately compromising the elegance in exchange for facilities on a limited UI or limited time. Now want to justify such a decision with "easy plain dumb rectangle is more elegant" is simply ridiculous.
Just between us, even when I have to do something as soon as possible I give myself the trouble to do something more decent than damn rectangles without even edges to serve as buttons as they are doing in interfaces like the Lollipop crap (Android 5.0).