To me, it's still, "hey let's wrap up the game setting in a new plot so we can make people play through it again." Of course, there are SOME areas that need to stay, KH2 did great with that, but so far as we can see, it's all stuff we have done before in Days.
I thought the same when I first heard about the game, but there seems to be enough diversity in missions and gameplay, plenty of new enemies and yes there's an entirely new and original story. I'm happy with it, especially since it's for the DS and looking very impressive indeed!
Okay so there are no new worlds, but I've got Birth By Sleep for that. Both games stand out in their own rights =).