I haven't been able to gather a WHOLE lot of info about this, but from what I did hear -

We get new clothing items
We get more weapons
The level cap is now 200
We keep the same base 3 classes, just more weapons
Much more content to keep us busy
Characters from PSU offline transfers to PSU:AotI offline

Not 100% sure about all of this, since I read most of it on a forum, where a guy was playing Japanese AotI. >__>;

That was enough to get me to preorder the game, though. o: