Once you’ve logged in, the most noticeable change to Windows is the new Ribbon interface on every Explorer window. At this stage, the Ribbon UI is in a pretty confused state and doesn’t seem to have some of its functionality, so it’s hard to tell exactly how successful this switch will be. Within Windows even suggests some disagreement may exist within Microsoft about using the new interface at all.
Also unclear is whether this change is permanent for all devices. The current build of Windows 8 has a toggle to return the toolbar and menus we’ve all grown accustomed to, but it’s not clear whether this will make it to the final version of Windows 8 or if it’s just a temporary measure while the design of the Ribbon gets ironed out.
This is a very early build, so many features, such as specialized tablet support, haven’t yet made their way in. Still, even this early on, we can say with some certainty that Windows 8 will bring some dramatic changes to the OS.