OK. Let's go with units. BFX adds new units for each faction. How many? FOUR. Four, really awesome units. But that's not all. The units CHANGE for each map. That means that maps have different unique units. Plus, to add even more, the skins for the units change for the map as well! It's really awesome. Wait...... did I say that already?
Gameplay has changed too. Guns are less accurate, and bullets do more damage. There is also weapon style changes and other stuff to complicated to explain.
Fun? YES! Let's just put it this way. If Lucas Arts came out with Battlefront 3 and it was EXACTLY like BFX, I would buy it. Go download it. NOW.