The overall concept isn't entirely awful, it's the implementation of the user interface, and the all too often lack of features or functionality that often requires reverting to "desktop mode" that savages the whole thing. The "not-metro" interface fails on so many basic, elementary user interface (now usually termed User eXperience) principles that it would be laughable if it weren't coming from Microsoft who in the past put a lot of good work into UX principles. They often ignored them in their own products, but that's a different problem.
One shouldn't have to randomly thumb areas of the screen in the hope that something, or anything, interesting happens. At the elemental level a user interface should be obvious, discoverable and consistent. Once "standards" are defined somehow, it is best to stick with them even if they are not the most optimal. For example, QWERTY has been proven to not be the most optimal keyboard layout for English language users, however it is an established standard. For mobile phones, pressing a home button is an accepted and expected method to wake up a device in order to use it, if there isn't such a button then the fallback is to press a button on the side, or at worst, top, edge of the device, this button will be a singular button on its own. On the other hand, pinch to zoom is not an obvious interaction method however it is an established standard interface and works very well and it's surprising how often even experienced users try it on devices or applications that don't support it.