Quick version: it looks good, mostly – no, wait, here’s how I summed it up for MacNN:

Testing this new beta is, actually, slightly weird: the Mac versions of Word and Excel now look like the iPad versions. That’s mostly true when you first start them up and they present a dialog box with New and Open options, plus templates. Choose one and go into it to edit the document, and the resemblance fades a little.

One thing that made the iOS version of Office a pleasure to use was that it was pared back, that some of Microsoft Office’s more esoteric features were removed. That even makes the Ribbon toolbar more useful, and this new Mac version also tries to balance features with a more minimalist look. We’ll have to see what it’s like after weeks and months of intense use, but at first blush it feels better than it was.

There are points where items seem a bit oversized: certain icons in the Ribbon feel excessive, and intro text as you set up the applications feels loud. That’s not a bad summary of the entire experience of using Microsoft Office 2016; it mostly looks better, Word feels good to write in, Excel feels powerful.

Hands On: Microsoft Office 2016 Preview (OS X) – William Gallagher, MacNN (6 March 2015)

If you’ve got a Mac and some time to kill, go get the Office 2016 preview here. It’s entirely free while it’s in beta and the best way to find out about anything is to use it. Do remember that it’s a beta, though: it’s not complete and it is always possible that you’ll lose work. So don’t do anything important in it.

Also, you could read the rest of my MacNN piece.