His main complaint is that it’s so different that it’s frustrating to existing users:
The Ribbon mimics the tabbed interfaces of the Firefox and Internet Explorer 7 browsers. It looks cool, but it took me most of five minutes to find, set, and test the Track Changes options my editor expects. As my deadline loomed, I panicked when I couldn’t find the option to save in Office 2003 format. It was hiding behind a new jewellike logo in the upper left corner called the Office Button.
Microsoft’s reviewer’s guide makes clear that all of the keystroke commands you know and love are still here. That will assuage speed-typing accountants who might otherwise refuse to switch. But as nice as the Ribbon and other user-interface upgrades are, it’s only natural that most users will react with annoyance rather than wonder when they find out they can’t switch to some kind of “Classic mode” in order to finish a write-up that was due 20 minutes ago (like this one).
This is always a big risk for UI designers. If you force users to re-learn how to use the application, why shouldn’t they just learn to use something else instead?
Here’s a link to the review.