A magnum opus and a swan song. The Nolan Brother's masterpiece accurately reflects the classic pre-silver age comics dichotomy of the battle of justice and chaos, of the immovable object vs the irresistible force, Batman vs Joker, in a way that was absolutely alien to Burton's 1989 treatment. As good a movie (and formative for the modern superhero film) as that was, Burton's flaw was that he discarded the books whole cloth, because he assumed they were children's entertainment and not guided by literary themes.
Heath Ledger's performance wasn't. It was a transformation, a possession by the character of the Joker.
This was, by far, the best Batman movie, and easily in the top-5 of comic book movies of all time (in no particular order, the other 4 that come to mind are Teenage Mutant Ninja Turtles (1990), Doctor Strange, Thor: Ragnarok, and Captain America: Civil War.)