Notably the main processor has been upgraded to an ATmega2560 giving 8 times the size of both flash and ram, amongst other things :)
Also there is a graphical LCD that should provide a larger, more user friendly display.
The extra serial ports (4 in total) will enable future expansions as and when required. One is dedicated to the USB for loading software as well as potentially being used to allow a computer to share the installed Xbee.
If you don’t want to use an Xbee, or want to use more than one, that’s fine- three of the serial ports are broken out to the left of the board. These could also be used for adding a GPS unit, or perhaps a bluetooth
to pc link for example.
Also broken out is the i2c port, so you can link it up to a magnetometer if need be (could make for simpler antenna tracking alignment)
A micro SD card will allow data logging, parameter saving, mission uploading and hopefully more!