As a casual user of the various Office apps, the ribbon bar is what made it usable. Before that, I'd make every attempt to keep out of Office.
Those who use it with any regularity likely know the keyboard shortcuts for things they use regularly, and the ribbon should work for finding the less common things in the same way it helps me as a casual user find everything.
It did. I couldn't find anything before the ribbon bar, frankly, and using tools took significantly more time because I had to search for them in overly long menus, or even submenus. Now they're mostly laid out directly in front of me, logically and visually ordered. I don't feel that menus are a good UI to anything.
It would seem that most UX people now agree with me, as traditional menu bars have been de-emphasised across nearly all the apps I use. Word was the only app which required me to delve into the menus in common use.
Why do you think the ribbon bar has a worse UX than a menu bar?
I love the ribbon. If you don't, try one of two things. One, try double-clicking on one of the headers - it'll make the ribbon hide unless you click it. This makes it effectively work like the old menus, except more horizontal and graphical instead of vertical.
The second is to scroll your mouse wheel while hovering over the ribbon.
Change does frighten and confuse people which is why the principle of least surprise is part of the human interface guidelines, but nobody seems to care about that anymore.
I don't know if I'd really say it's worse, except for that it breaks the standard expectation and user interfaces are supposed to follow a uniform design on one environment, but it's a change and I prefer interfaces not to change.
Those who use it with any regularity likely know the keyboard shortcuts for things they use regularly, and the ribbon should work for finding the less common things in the same way it helps me as a casual user find everything.