I dont know about the technical aspects of the FADEC system, but from a pilots point of view there isn't much difference.
Basically instead of using the steel cable from the throttles to the engine it uses wires (sort of fly-by-wire I guess).
They system is better able to optimise engine efficiency giving a fuel saving of 0.5-1.0% over an EEC.
Another added benifit is that if the thrust levers are in the same position the system will command both engines to generate the same thrust, so no more staggered thrust levers!