Think the whole comic book superhero genre is inherently silly and that silliness has always been a barrier between you and trying to enjoy what that genre has to offer?
Had your life destroyed by mental illness?
Feel like you're a piece of human garbage, beyond and undeserving of redemption?
Then by golly is Harley Quinn a cartoon for you!
It is a series that is at once both respectful of its source material while also acknowledging it is a genre that is indeed inherently silly if you try to take it too seriously. It's also a show that examines different people coping with mental illness in different ways. Some of them cope in healthy ways and some of them cope in unhealthy ways but ultimately their success or failure is measured by whether or not they've grown.
It's a series that doesn't even try to hide the fact it's a cartoon, that its premise is utterly and completely silly. It is a cartoon that makes it clear that if all these people were actually real live people living in our real live world they would be horribly toxic, dangerous people that would need to be locked up for their own protection and for the protection of society. The violence is over the top as is everything else about the show. Between the swearing and the violence it assumes that you, the viewer, are an adult capable of adult thought and that you know if you were to emulate any of these people in the real world you would be a terrible, terrible person. It assumes you are smart enough to figure at least that much about it for yourself and when you meet that show halfway, when you accept these are cartoon characters living in a silly cartoon world and that their actions are completely unacceptable anywhere outside that silly, cartoon world then when you've made that compromise it's a show that has something to teach you.
It's a show very similar to other adult cartoons, shows like Archer and Rick and Morty where everybody in the show is an asshole who is miserable but when you strip away their egos and pretensions you understand the reason they're miserable is because they're assholes. They're the architects of 90% of their own misery. What sets Harley Quinn apart from these other shows is while Archer and R&M are about having fun watching assholes being assholes to each other, Harley Quinn shows that even assholes reach a point where they become tired of being assholes. The characters in Harley Quinn start to realize "wait... maybe I'm the one with the problem" and when they do realize that they have a choice, and they are the only ones who get to chose what to do at this point. Do I put my ego aside and try to grow and hopefully decrease the amount of misery in my life and the lives of everyone around me or do I just dig my heels in, act like a petulant child and continue my self-destructive behaviour because I'm too angry at everything and all I want is for people to hurt like I hurt.
Everyone's endpoint in the series is ultimately the results of the effort they put into growing. Batman learns he has to let other people into his life. He can't just be the stoic rock that everyone else leans on. He has to sometimes lean on other people and he has to learn that leaning on other people isn't a weakness, it's life. Ivy has to learn that human beings aren't garbage. She can't just retreat into her world of plants and expect to be happy because human beings are just too hard to understand. Both Harley and Kiteman help her come to that realization but ultimately the responsibility to grow is on her shoulders. She lets them help her along the way because she knows she's not coping with her intimacy problems in a way that is healthy and that is a choice she makes. Doctor Psycho even grows, not as much as the other character but he does grow, but then he stopped growing. He dug his heels in and had a tantrum and in the end he was the one who suffered because of his actions. He's the one who ended up locked up in Arkham and hopefully if the series gets renewed for a 3rd season we will revisit his character and show yes even a shit-heel like him can become a better person if he, as an adult accepts responsibility for his actions and takes agency over his own life and tries to grow instead of being an angry little man blaming everyone else for his problems and never once pausing to wonder "wait... am I the asshole here?". Even Kiteman learns he can't be a doormat. He can't be constantly seeking everyone's approval. Not his parents, not his lover. He learns that people won't see his worth until he himself can see his worth. Kites are for soaring, not for being walked upon.
But ultimately the biggest growth story is that which happens to the titular Harley Quinn and her once-lover the Joker. The series starts with Harley finally coming to realize (through the help of her friends) that she is in a toxic, co-dependent relationship and that she can't "save" the Joker. She can't fix him if he doesn't see he has a problem needing fixing. She can't fix him because she hasn't even tried to fix herself. She needed the Joker because he was a distraction from the fact that she herself is a very fucked up person. Neither one of them could grow until they ended their toxic relationship. Once they excepted their relationship was toxic and once they moved on they were able to grow. They both learned what love is. The Joker is now a suburban step-dad and god help the person who fucks with his kids or girlfriend. The Joker came to realize "wow, I was the asshole wasn't I, well time to do something about that". When he did that he became a sympathetic character. He was no longer obsessed with "how dare Harley leave me, I'm the fucking Joker". He knew why she had to leave him and when he came to understand, he understood that sometimes love means you have to let someone go and that just because a relationship doesn't work one way doesn't mean it can't work in others. Ultimately he and Harley part as two people who still love each other but it's a love of mutual respect and friendship and that is a valid form of love and non-romantic love is still love.
Harley learns that she can't fix anyone until she works on fixing herself. Harley learns that being a manic pixie dream girl isn't cute if your mania brings misery into the lives of the people around you. Harley learns that while her fucked up parents and her co-dependent relationship with the Joker contributed to her misery that she is a rational adult who ultimately is the only person who can make her life whole. She takes responsibility for her actions and puts in the effort to make life better for herself and her friends.
How much the characters grow depends entirely upon them. Do they stop to examine themselves and become self aware or do they sulk and blame everything and everyone around them for their misery? Do they make a conscious effort to do better than they did the day before? They all grow or don't grow based on the effort they can and do put into growth and the ones who do the work reap the benefits and the ones who don't wind up angry and alone.
So if you are a person who has always hated the superhero genre because of its silliness then please give Harley Quinn a try because it fully admits it's silly as fuck. I mean Harley uses an A-bomb to blackmail the city into building an awesome real-life hotwheel track dedicated to her (which she destroys herself when she comes to realize there are things more important than her own ego). That is just so silly, but it was entertaining too.
If you're a person who has had your life impacted by mental illness, either your own or one suffered by a loved one, then you should really give Harley Quinn a watch because that's what the show is ultimately about.
If you think you're too damaged a person to grow, if you think you're too shitty a person to be allowed to grow then boy do you really need to watch this show because if the fucking Joker can grow as a person then guess what, you can too. Growth isn't something you do and are done with. It's a continual process and nobody grows at the same rate, what is important is that you continue the process and not dig in your heels and have a tantrum because the process is hard, or other people seem to be able to do it easier than you. Like King Shark said "baby steps".