I had a problem with formulae not showing properly when I opened them in Word on a Mac. In the past I've also had problems with spreadsheets that depend upon macros that don't survive the translation process to the OS X version of the software. If harryb2448 is right that the 2016 version is much closer to what the Windows users get, maybe these problems are all in the past, though. (I get a full copy of MS Office for £9, under my employer's 'Home Computer User Scheme' - and I'd say that this is a fair price, given some of the iffy Microsoft products I've had over the years.)
Workarounds I've used in the past include sending the documents I needed to view to a hotmail account, and then opening them in the online version of word (which meant I got to see the complex formulae properly) and my old favourite, Libre Office. (That's also useful when I'm trying to open my old, old Claris Works documents, and things like that... and it has the advantage of being free, so it's worth a try, right?)