Overall Windows 8 is extremely jarring right now from a desktop user perspective. Metro is the Windows shell, no ifs ands or butts. Metro applications can only be accessed through the Metro shell (i.e. the Start Screen), and the Metro shell is always what the tablet will boot up into. Explorer as we know it is the Metro shell – if you kill it, you kill Metro shell with it – so at this time it’s not possible to boot up into the traditional Windows desktop. Even if you could, the Start Menu is gone, replaced with Metro charms.
So what we’re really evaluating is the ability to use the Metro shell and Metro applications with a mouse. For all the good Microsoft has done implementing multi-touch, the mouse has clearly suffered as it currently stands. Click & drag does not operate the same as tap & drag, which creates some oddities when you want to scroll around. In fact scrolling is probably the biggest oversight right now, as the Metro style dictates applications are laid out left-to-right rather than top-to-bottom. The mouse wheel will (slowly) scroll through tiles on the Start Screen, but in other places such as the Microsoft BUILD application the mouse wheel is useless. In its place you have to drag a scroll bar around, which is about as fun as it was prior to mice coming with a wheel. (Source