Today is a good day, because today I once more get to talk about Star Wars. This episode referencing Empire Strikes Back is easily the most direct Star Wars reference in the show. And not only does Aang leave his training without finishing it, but he also gets a vision of his friends in danger. It's basically a 1 to 1 comparison and I love it.
I also love how Aang points out the apparent contradiction in the 7th chakra. Like the Jedi teachings, he's supposed to have no earthly attachments, yet also feel love according to an earlier chakra. It's the exact same point Anakin makes in I believe Attack of the Clones, to show one of the flaws in the Jedi teachings. And in the case of Star Wars, it's Luke's attachment to his father that gives Vader the chance to redeem himself, bringing balance to the force.
And my god the scene where Toph literally invents Metalbending is so well executed. The Guru's dialogue over the scene makes it really come together.