I like the fact that the main content on the page never disappears, although the interacting with the side bar is at an all time high. It& a very clean layout with flat ui colors that speaks nicely to the flow of the app.
Design is a huge part of UX, acronym for User Experience. This is the very reason why a lot of designers think that a good UI or user interface makes up for a good user experience. This however, is not true.