With Google releasing Android 4.3 recently, we've viewed it as more of an intermittent update rather than new features being added. With some digging it looks like a small SMS feature has been unearthed with the ability of 3rd party SMS applications being able to send “quick responses” upon rejecting an incoming call. Although for this to work, the 3rd party application that's in use has to be updated first in order to take advantage of this new feature.
Another added feature is that Android 4.3 now allows notifications to be read easier by applications such as Light Flow. While Light Flow works wonders for a lot, it is also quite buggy due to Android failing to read the notifications correctly. Once Light Flow and other apps like it update with Google's new fixes, things should be a whole lot smoother.
source: Android Central
I know what doesn’t work on 4.3…the .33 radios for lte on the nexus 4….lte works but you can make phone calls with .33 radios on 4.3
And it doesn’t work with CM 10.2(4.3) either .grrr