The ribbon interface was a key feature of Microsoft Office 2007. It was criticized because of its unfamiliarity but also because of its inflexibility. In the 2010 version, the ribbon layout is more familiar simply because it is no longer new. However, Microsoft has gone further allowing users to move functions or groups of functions from one ribbon to another. (See Ribbon Customization Options in Office 2010.)
Similarly, the 2007 file formats are retained: whilst this does not provide file compatibility with older versions, the passage of time and no further change means that doing nothing is almost a feature in its own right!
The most radical surgery to the interface comes with the reinstatement of the File menu. This is a major U-turn but the menu is much more powerful than the 2003 file menu with big glossy dialog boxes, known as the Backstage view, covering functions such as Print and Save.
These changes together with the full integration of the Outlook and OneNote applications are key to acceptance of the new release, and may be enough to trigger upgrades form those who resisted upgrading to Office 2007. As one who never willingly embraced Office 2007, speaking personally, the new interface features are a huge improvement over the 2007 release.