From a first glace, the most noticeable change in Office 15 is the fusion of Ribbon and Metro user interfaces. Microsoft's Ribbon graphical user interface was first introduced with Office 2007 and has been reported over the years as "taking too much time and patience to learn." Nevertheless, Microsoft has given its contentious Ribbon interface a facelift by fusing it together with Metro UI, which will be featured in the upcoming Windows 8 operating system.
The ribbon itself will now default to being collapsed, and most of the gradients, panels, and dividing lines prevalent in Office 2010 have been removed with the new release. Office 15 takes a different design approach by minimizing ribbons by default and employing a fullscreen "backstage" menu with left-side navigation controls. Of course, the interface is subject to change as this is an early preview of the development process. We expect the public beta releasing this summer will feature substantial changes.
More pictures can be found at The Verge.