Vanitas:

Pixar's worlds got the best treatment when it came to not just Disney worlds in 3, but in general with Disney worlds. Most of the time, especially in 3, they're either shitty rehashes of the movie with the KH plot wedged into it or pretty forgettable original plots. Toy Story and Monsters Inc, on the other hand, got great levels(Granted, I would've preferred more exploration through the doors then going through the factory, but eh), good interactions between the Pixar and main trio with the partners for the world actually feeling like they actually end up being good friends with the trio, some pretty neat designs for enemies(Also the best Unversed designs, but that's not saying much), some nice nods to the movies the levels are based on, and the KH villains not only work well with the plot of the world but also tie in pretty well with the main plot as well as having the partners for those worlds actually interact with the KH villains. Woody telling Young Xehanort no one must have ever loved him and Sully having none of Van's bullshit is the kind of thing I want to see in Disney worlds in Kingdom Hearts games.

Also, Toybox is just an awesome level, period(Barring that boss at the end. But even then, it's arena is cool).