First 30 second impression of the movie

Gotham happens when rich people, governments, businesses, aren't doing their job, driving the economy the way they should.
Papa Wayne is every charismatic rich man ever, giving great hopes yet coming through on only a few of them.
Phoenix plays the part beautifully primarily because of the acting he does when he isn't acting.
The acting that happens when he is absolutely silent yet has to convey emotions without words or gestures

Validation and self-esteem

Arthur is seeking validation, him dancing, him dreaming of being on the Murry show, him dreaming of Murry calling him a son for whom he would be willing to give away all his fame and fortune.
Its about a person seeking recognition by the masses and of course acceptance by his very own father.
Perhaps most vividly seen in him watching himself on television.

Arthurs dance

His unique celebratory / preparation dance reminded me of primal mating rituals. Like a peacock seeking favourable female glances, spending arms in a swirly motion, asserting his dominance in gaining attention

Physical state affecting mental state

The rapid descension of Arthur's mind set against the rapid descension of Arthur's mind just goes to show how much one's social and environmental surrounding can affect an already ailing mind. The part that got me was the city being infested by 'deadly rats' as if poverty wasn't enough.

Divide in rich and poor

Playing devils advocate here for a minute. I'd like to argue that it is dumb when poor / working class folks get angry at rich for being rich. One could also go so far as saying it is the rich that provide jobs (and hence livelihood) to the poor. As seen in the movie, the state of the city was in ruins once the mask clad men had taken over the city. Imagine, would you dare raise your child in such an environment?
I do not encourage the greed or selfishness of the rich in any way. Yet, I find the idea of Joker as a Mayor or state economic adviser to be not so savory

Calming the crowds through pubic comedy

It almost felt like Mr. Murry too was controlled by the state. Like a state appointed pasifier of sorts for people of Arkham. To calm and deflect the attention of the people from the true trials and troubles of the masses and sick city they exist in.

tobacco smoking kills 70 lack how many does mental illness does

trajedy is spectacle just like the movie network

Recommendations

If you loved the movie because of Joker's (Joaquin Phoenix) performance, you should absolutely check out The Master (2012).
Why? well, because in this movie he is basically acting out a piece of his own life. The movie is about a man who leads a cult, unbeknownst to you perhaos, younger Joaquin himself was a part of an actual cult. You do the math.
If you loved it for the plot you should totally check out The Network (1976)
Another personal favourite is Taxi Driver (1976) which producer Martin Scorsese himself sights as inspiration for the movie

Each of these movies are a part of my all time favourites collection and I recommend you watch them even if you enjoyed just a sliver of Joker.