Above is a video essay detailing the many reasons what makes The Joker such a great antagonist in The Dark Knight. This video essay also includes some great comparisons to other movies to compare their stories and villains. It discusses how The Joker is designed as the perfect villain to accompany Batman. I think that this also extends to The Joker being the perfect villain for the city itself. Gotham’s greatest danger comes in the form of two ferry boats full of people in danger of dying. This scene goes in line with The Joker forcing Batman to make decisions and show his true self like when he forced Batman to choose between Harvey and Rachel. In the ferry sequence, The Joker does this to the people on these boats. He is forcing them to make a decision that will show who they truly are by blowing up the other boat and saving themselves. In the end, just like Batman, these people actually grow stronger and learn from the experience.
Another interesting point about this sequence at the end that this video essay brings up is how much is actually at stake. In movies like Man of Steel, Superman is fighting to stop destruction of the entire Planet Earth. However, we know as the audience that he will be successful in stopping that from happening because we know there will be a sequel. In The Dark Knight, the lives of a few hundred people on two ferry boats are at stake. We are allowed to grow attached to these characters, but none of them are Batman. They could very easily die and The Dark Knight still have a sequel, like The Empire Strikes Back. This adds much more weight to the sequence and suspense.