The setting
I know it's tempting to want to make this into a full-length movie, but I love how the video can say so much in 7 minutes.
What I'd really like to see his a full length movie that uses the same setting. The backgrounds, both in the city and outside in the abadonded town, are amazing, and I can't think of any other shows with domed cities that are as beautiful. THe only ones are Big O and Ergo Proxy, but they're more dystopian or at least more negative than utopian.
(I know it doesn't seem like a utopia, but I like how there are no more suburbs and everyone lives in cities and how nature is finally getting the chance to heal itself. Then again, Miyazaki did say that people tend to turn to things like cults or opressive governments or frivolity to distract themselves in situations like that.)