Has somebody put together a changelog yet?
The only real change I've seen so far (outside of them updating the icon to be blue) is there is now a big button for Steam Guard in the main menu. Going to this menu leads to some text that suggests you can use the Steam app as a mobile authenticator, but when I try to enable it the only option it gives me is to use email for 2 factor authentication (or to disable it). Not sure if the mobile authenticator functionality hasn't been enabled yet, or if I'm just missing something.