Installed on someone's laptop as they insisted on having the latest when offered the choice. Called in to help them with their CV... there's a border round it that shouldn't be there. I've torn my hair out trying to use it. I had to do the typical repair job on someone who's cv says they are proficient in Word, yet they add spaces below paragraphs by adding more paragraphs, right aligned words by careful use of spaces (proportional font as well, so it's almost but not quite aligned), written the whole thing inside a table cell, used a mix of numbered and unnumbered bullet points and bullet characters, mixed margin positions... Basically the sort of a document I used to get from a certain professor to make ready for journal submission. It would usually take about an hour per 1,000 words to reformat and make pretty (printed on paper of course it doesn't look like you've done anything during that time, but hey ho!)
Office 365... I gave up. The most unwieldily piece of crap I've ever come across. Highlights words at random when click-dragging a selection, throws grammar errors all over the place, show invisibles doesn't show all invisibles any more, format paragraph has gone somewhere I can't find, all the tools have moved around, save takes you into some other screen full of crap about licenses and file info that you just don't need to see, the "ribbon" thing just takes up screen space and things seem to jump around from one place to another in it depending on what you're doing, margins and reflows suck major league, the tabs and arrows behave unpredictably...
In short, if this is M$ idea of productivity software, they've written themselves a new dictionary. And I don't hold out ANY hope for Windows 10 being any better. I criticise it with the prime example that any OS which requires prerequisite knowledge that swiping your finger from the right off the trackpad or your pointer from the right edge of the screen, leftwards, in order to bring up a hidden menu of control panels has just pissed all over Xerox Parc's decades of work on human/machine interaction whilst laughing maniacally and rogering themselves up the anus with a spiked baguette in a sadomasochistic orgy.
I recently had to level the same accusation at Apple for (by default) hiding the scroll bars when your pointer isn't in a magic 1/8" strip down the side of a window.