When it works, the collaborative editing features are nice. It’s good to be able to do that in the native app rather than a browser.
It rarely works – but it's miles better than “this file has been locked for editing by somebody else”, so I'd still call it an improvement over 2010. (Just not an improvement over its competitors.)
I have a few collaborators with whom it’s not really feasible due to incompatible versions, but mostly it works for me.