Now, with the sequel, Media Molecule is taking the concept even further and giving players the ability to create their own stories and link their levels together. Check it out (The video is really small, for a larger HD version, click here):
How they plan to allow people to create their own stories isn't really clear yet, but however they do it, it's going to open up a lot more in the realm of possibility than the first game did. Players can create something even more unique to themselves and their creativity than any other game I've seen (Not that I've seen an overwhelming number of games that foster creativity in the player), and hopefully people will come up with awesome ideas that will expand our imaginations in some way.