Disclaimer: I've only used the preview version, not the release.
I preferred the UI for Office 2010 — 2013's ribbon looks a bit too dull and needs some more borders to distinguish groups, in my opinion. The animations in 2013 are great, though. Cloud integration in 2013 works really nicely, and integration is seamless (like iCloud+iWork) but also flexible (unlike iCloud+iWork).
Chekka: The ribbon can hardly be called "minimalist," but despite my initial frustrations, I much prefer it to the old UI, particularly now that it's fully customisable. It makes me
want to use Office over alternatives like OpenOffice. It was only a matter of time before MS abolished the abomination that was the old Office UI, i.e. a ton of cluttered menus, and a ton of cluttered toolbars containing a ton of icons. It made no sense except to those who had it burnt into their brains through years of use.