3.8 brings together several of the features as plugins projects and while this isnít our first rodeo, expect this to be more beta than usual. The headline things to test out in this release are:
The new admin design, especially the responsive aspect of it. Try it out on different devices and browsers, see how it goes, especially the more complex pages like widgets or seldom-looked-at-places like Press This. Color schemes, which you can change on your profile, have also been spruced up.
The dashboard homepage has been refreshed, poke and prod it.
Choosing themes under Appearance is completely different, try to break it however possible.