It also makes shortcuts discoverable! Just hit the alt-key and virtually every thing pops up with it hot key. Hitting alt in a standard windows app only tells me what menus are available, not which actions are available.
Ok, maybe shortcuts are discoverable, but actual actions no longer are. Not everyone finds the ribbon an improvement; I feel the need to point that out since so many comments appeared praising the awfully opaque ribbon.
My disability means that I have to read through every single option, verbalizing it. Changing the layout that I know so well has meant that MS Office is no longer on the list of applications I bother with.
I know where everything is in Libre Office, it's quicker and less stressful to use. A number of people have told me that it's too bad, I'll just have to learn the new system. Honestly? I really don't care what those Microsoft fanboys think. The "new" system is just far too much work for me to be bothered re-learning. Libre Office/Open Office is more than good enough.
In my opinion yes. Or rather, Windows users have had decades being trained to find certain functionality under certain menu options to the degree that most will do it by second nature irrespective of the application they're in. The ribbon menu throws all that muscle memory away and leaves you trying to find it again in an interface that no other applications use.
I don't frequently need to use office products but when I do I find them absolutely infuriating.
The "no other applications use" is not strictly true anymore, and hasn't been for a while - most stock Windows apps use Ribbon now, even Explorer.
But in general, the problem that you (and the other adjacent comment) is describing is different - you're not talking about discoverability so much so as learned muscle memory. Obviously, changes do break that, but this doesn't necessarily imply that for a new user, discoverability is worse. You'd need to run a study to determine that.