Style over substance, but fantastic style! Every time the joker is walking anywhere, we get pounding, ominous music, and a variety of shots. Yet you step back and realize its a crazy guy that lives with his mother walking down the street to his dead end job. The movie would stay an introspective portrait of mental illness until an awkward and forced plot twist gives the movie some legs. Sorry if this is a spoiler, but the basic backdrop of the movie is that a crazy guy in a clown mask who talks to himself on the bus and laughs uncontrollably gets fucked with all the time on the street by bullies, until he shoots and kills some assholes bullying and beating him up on the subway. When the news reports that the deceased were rich stock assholes or something that worked for Wayne industries, the entire city begins putting on clown masks and chanting "Kill the rich", because of a depressed economy, making the nutcase a cult, underground hero, sort of in the traditional of Natural Born Killers, but without the good script, logical plot points and character development. But if you can just sit back with popcorn(especially with a little cannabis butter on it), you will get into a very strong method performance by Phoenix, and a VERY good musical score and direction, that creates an intensity that carries the film when the script cannot.
By the way, as several have mentioned, the film HEAVILY borrows from its ancestors like King of Comedy, Taxi Driver and even Network. Even an implicit reference to Bernard Goetz and the subway murders of the 80s.
