So, you want to know about everything that's new in Android 4.3. Every single change that's occurred since 4.2.2. Well, if you don't mind scrolling through a barely-human-readable, mile-long developer changelog, now you can satisfy that urge.
Al Sutton has posted a wonderfully-formatted AOSP commit changelog covering the changes from Android 4.2.2 (JDQ39) to Android 4.3_r2.1 (JSS15J). The JSS15J build is the most recent release of 4.3, and is the one currently shipping on the new Nexus 7.