Have a look at my short video (only 4 minutes!) on the new user interface for document libraries in SharePoint.
Like many the first I heard of this was in the Office 365 Yammer network (access required) and was pretty surprised. I do like the main part of the doc library now as it brings a consistency to documents between One Drive and SharePoint. It removes the familiar SharePoint UI though which means a little retraining for users.
Not much thankfully, but it will cause confusion. One other thing is that on the left hand navigation menu of the site when in the document library, it shows both the quick launch and top level global navigation as one list which is clunky and would be unworkable on any large site. I think it’s a bit of ‘two steps forward and one step back’ for Microsoft on this one. And read on below for other views of the changes.
And here area few other articles about the changes.