Decent on a touchscreen interface with its philosophy of big images and text to accomodate physically smaller displays. De-emphasis on multitasking and pretty GUIs to conserve battery life via lower CPU usage which might be useful on mobile devices like tablets and smartphones but is terrible for productivity.
Outright terrible on traditional desktops/laptops due to horridly low information density on physically larger displays, multitasking being essential on desktops/laptops for any level of productivity, and touchscreen interaction translating horribly to desktop form factors (laptops might be a hit-or-miss).
Hello Apple! With Metro only allowing installation of software from the Windows Store, where only software specifically approved by Microsoft can be listed, the Windows Store harbors the coming of a closed platform and ecosystem for Windows in the years to come; absolutely horrible from both ethical and practical POVs.