In addition to the (relatively freakish) second UI, there are a bunch of minor-but-welcome enhancements that I keep stumbling across. For instance, I right clicked an .iso, and the default OS can finally mount it. Double click a PDF file -- wow! I can see the contents without installing anything.
Several little things like this, that have previously made using Windows so much more painful than OS X, are addressed in Windows 8. I haven't really seen any major improvements over Windows 7, but minor improvements still can make life nicer.
EDIT: Oh yeah, the desktop pictures! For so many years MS exhibited horrible taste, by default slopping a huge, ugly Windows ad all over the user's desktop (Win 7). In XP, they had that crappy picture of a field near the Microsoft campus that some random employee shot. In Windows 8, I get a steady rotation of beautiful, professionally done photographs that rotate periodically, and really blow away the (previously bar-setting) default desktop pics that Apple ships. Not that desktop pics are a huge deal, but again it is one less thing I have to change about the default installation (can't stand looking at the ugly Windows ad from Win 7).
Several little things like this, that have previously made using Windows so much more painful than OS X, are addressed in Windows 8. I haven't really seen any major improvements over Windows 7, but minor improvements still can make life nicer.