This is the Big Picture interface. It's much cleaner, with much larger icons that are far easier to see from a comfortable TV-viewing distance.
The main screen of Big Picture mode has three options: Store, Library and Community. This cuts out the News tab that's available in the regular Steam interface, streamlining things significantly.
The player's user icon is shown in the top left corner along with notifications, while the other top corner shows a settings icon, the Big Picture toggle button, and a link to beta information.