*SPOILERS FOR BOTH MOVIES*
I liked it pretty well. I find it well represents the struggles of a man who wanted to make a change but got in over his head. In the first movie, Arthur is someone who's had a hard time. He looks around and sees people who only care about themselves and shows that he doesn't like it. He kills the men because he saw that they thought they were better than him and thought they were invincible compared to a lowly freak like him. Once he shows them that he has more power, they run like cowards. He wants people to see the humanity in each other and not care about how much power other people have.
What happens in the second movie, he has this whole group of supporters that think that he stands for bringing down the upper class, the suppressors of the city. He doesn't though, he just wants people to be civil and care about one another. This constant clash of himself with his supporters, himself with the people who believe that he's a freak and shouldn't live (the people he hates, who have more power than him and who think they're better than him) and the him with the person who people want him to be drives him into a hallucination with Harley Quinn and he sees her as the only person who cares about him. This is where the musical element plays in. He is imagining that he's the host/the star of the world and not some lowly nobody. As he starts to envelope himself into more of the fantasy that Harley and his supporters have of him, he becomes more and more like the joker that people think him to be, the one who wants to tear down the people who don't care about him and think they're better (a good example of this is him defending himself and calls out the guards who make fun of him). Eventually, he realizes that the person who killed the people in the first movie is not the person who he is trying to be. He is not the joker. This is what Harley means when she says "You broke the fantasy".
I believe this film is even better than the first one. I understand how people don't like looking too deep into media and only take it at face value, but you can't do that and say that it's horrible. Open your eyes and read the title, "Folie à Deux" is literally French for "Folie for two" or "Madness of two". Harley and Arthur are both crazy and this movie literally points it out in the title.