Well, I don't know for sure how long they've been working on it, but there's certainly been a lot of time since the last ones -- so they could have definitely put a lot of work into it to make it awesome. There was also the Japan-exclusive KH title a few years back that looked amazing, though of course I didn't get a chance to play it.
I don't know that I'm necessarily expecting it to be the best in the series, but I suspect it'll be a very strong title. Even Chain of Memories was quite good despite the wonky combat system, and I look forward to playing the new version in KH1.5. But, yeah, all I really want from KH3: An interesting story, creative new worlds, enjoyable game play. I don't need it to be revolutionary, I just need it to be competent.