I don't think it improves accessibility when I keep having to go hunting in different sections for the right button. (The ribbon in the Recycle Bin makes no sense to me either.)
I'll admit it can be daunting for a new user to see a lot of buttons, but if there is a tooltip or even a tutorial for each button showing where it can be useful, that shouldn't be much of a problem.
For me, the Ribbon is what made Office unusable. I've used MS apps since the MS-DOS and Xenix days. I remember the old MS menus (2 lines, bottom of screen, summoned with Esc) to CUA transition, then the horror of WinWord 1, then the passable WinWord 2, then the actually quite nice WinWord 6.
I still run Word 97 on Ubuntu under WINE. Works perfectly.
But after Office 2007, it is totally unusable for me.
I did say "But then I'm not sure if that was just a case of getting used to the new layout" - still open to that being the case.
Maybe it's like 12th edition text books, change for the sake of change. In the case of Office software, we need people to keep needing the 'basic' and 'intermediate' training sessions; we need credentials to justifiably decay with time?
I'd say something like the "ribbon toolbar" upgrade of MS Office, which I think improved accessibility of functions, is one of the only examples I can think of. But then I'm not sure if that was just a case of getting used to the new layout.
Windows "Settings" versus the Control Panel is a counter example. It was a downgrade, it still sucks now, years later, but the Control Panel could be argued as 'dated' by some definitions.