The ribbon is just awful.
The thing is, it's not a bad toolbar replacement, but it is an absolutely dreadful menu replacement.
No, it's a crap toolbar replacement too: (i) they removed all ability to customise it and (ii) you can't show things from more than one "category" at once, meaning that a lot of things that used to be 1 click away are now 2 clicks away. Seriously, what POSSIBLE reason is there to stop people from customizing the toolbars/menus to make them work the way THEY want them to?
Add on top of that the changes it implies to keyboard shortcuts (and just to really mess with the users, they decided to make it so that *some* of the old shortcuts still work but with no predictable way of telling which ones... and of course for the shortcuts which were based on the old menus you now lose the visual cues that you used to have).
And that's just the issues with Ribbon as a concept. The implementation is awful too... many things just not in anything like the "logical" place (I've resorted to just googling what I want to do immediately if the old keyboard shortcut doesn't work now, it's quicker). My workplace switched to 2007 over 12 months ago and people are *STILL* struggling every day to find things which used to be easy.