[spoiler-free review; spoiler-filled review will come some time around the weekend]
Joker is not a superhero/supervillain film, but a political drama film. There is no massive explosive scene or many special effect, but that does not mean there is the violence in it. There is violence everywhere in Joker, because the world is a fucked-up place.
There is a lot of political unrest in the film, and we have mixed feelings watching it after months of protests in Hong Kong. The film throws in many political elements into the film, like "We are the 99%" from Occupy movement, the idea of just and unjust changes over time and media's control over the views of the masses. There is a lot to dig in, and looks through the appearance of the film and see what is really causing the problem in the city which is a reflection of our world.
Joaquin Phoenix has done an Oscar-winning job portraying a man with mental illness, and the origin of his unfortunate plays a major part of the film's story.
Todd Phillips has condensed complex political ideas into a drama film using familiar characters to speed up the pace of story-telling, while paying tribute to Christopher Nolan's The Dark Knight and Zack Snyder's Watchmen.
One more thing, there is no Batman.