The full list of features which will be offered with the new update follow:
- OpenGL 3.0 Support
- GALAXY GEAR Support
- TRIM Support (Makes the device much faster)
- ANT+ Support
- Samsung KNOX Implementation (KNOX bootloader and dedicated application)
- Samsung Wallet comes pre-loaded
- Improved RAM management
- Improved Display colour reproduction (Display looks much sharper than before)
- Improved TouchWiz Launcher (Much less launcher redraws and less lag)
- New Samsung Keyboard
- New Samsung Browser (Full screen by default, new tab interface and more)
- New Reading Mode (Optimises display for reading, used by only a few specific applications)
- New Camera firmware
- Minor UI tweaks (Contacts app, Flashlight Widget, dialog boxes etc)
It looks like the Android 4.3 update also significantly improves the performance on the Galaxy S4, with synthetic benchmarks measuring up to 20% increase. Check out the table below that the folks over at the dedicated Sammobile created, listing the state of the Android 4.3 update for the Galaxy S4 on different carriers if you are interested:
source - SamMobile