The following comments come straight from director Tetsuya Nomura...

On story...

"It's a bit complex, but basically there are worlds that fell into darkness besides the ones Sora returned to normal in the first Kingdom Hearts -- some of the princesses' worlds, Dumbo's world, and so on. The original story had all these worlds get fixed up in KH1's ending, but not all of them completely returned to normal, instead lying in stasis between light and dark. Since the worlds themselves are asleep, the game is set in the dreams these worlds are having. It's Sora and Riku's job to wake these worlds up, return them to normal, and gain their Keyblade Master certification."

On Sora back in his KH1 outfit...

"That's because he is entering the dreams of these sleeping worlds. It also has to do with the fact that Master Yen Sid told him that he needed to completely re-learn how to use his Keyblade, to go away from the self-taught approach he had been using. Sora doesn't think that's necessary, but Riku, his confidence low due to having been taken in by the darkness before, agrees to it. Thus Sora comes along with him on this quest."

On the Dream Eaters...

"Since there are no Heartless, the Dream Eaters consume dreams in these sleeping worlds instead. Sora has to use them in order to travel between worlds, and they relate to his abilities as well -- raising them directly connects to Sora and Riku's improving as fighters. You can bring only two into a battle, but try hard enough and you can collect them all if you like. I can't say exactly how many there are, but they will number in the tens."

On Traverse Town...

"When you first enter Traverse Town you have the same basic member set. We wanted to get some fresh characters in there, so that is where Neku and the others come in. Neku has been separated from Shiki, his usual companion; we'll have more to say about her and the other characters later."