Office is really great on Windows, no questions asked (at least for me, I think it's vastly superiors compared to Libre/Google Docs/iWorks), but on Mac? Holy hell.
I bought Office 365 (or rented) and used the 2016 preview on OS X before and encounter constant (!) crashes up to the point that my personal cash management (which unfortunately relies on some excel-functionality) doesn't work anymore. Like, at all. As soon as I change a certain field (which happens to be the current bank statement, btw), Excel freezes and crashes.
The cloud functionality is a privacy nightmare and only allows Microsoft's cloud and Dropbox as source, so owncloud (which I personally use) or any other semi-popular service isn't available. Also, it works like SharePoint - if you happen to "lock" a file (by leaving a desktop version of the file open somewhere), you can't edit it elsewhere (including the web UI). And yep, that's what they call "collaborative features".
...and last but not least, Outlook can't connect to my IMAP (Zoho) anymore w/o any error message. Just tells me it ain't connected.