''Empty worlds'' wouldn't be much of an issue if there was a good element of exploration. KH1 had it best but even then it was riddled with less than perfect platforming. They really could use some fresh take on the level design. I still think one of the best things KH3 could add is some sort of dungeons be it optional or mandatory (or both of course). Hidden treasure and challenging fights. KH1 is actually perhaps the worst when it comes to mandatory encounter design against normal enemies, go figure.
Honestly one thing I am afraid is that the pressure of ''next gen KH'' could hurt the level design. I just wish they got some level designers with a passion for this kind of stuff and worried about the visual stuff after.
What KH3 should be:
What KH3 probably will be is huuuge empty areas with insane amount of enemies, heartless tornadoes and whatnot and enough room to justify over the top Disney ride summons. Oh well. FPS genre transformed from dungeony designs to open world and that is fine but I think an action game like KH (that isn't 100% action focused like DMC or something) could really benefit from some more complex levels. I'd like something akin to the Arkham games maybe? ''Big'' open areas that you start with to go explore different smaller and more design heavy areas.