I'm going to save you some time and semi spoil the movie (spoiler at the end). This movie is so terrible it ruins the first one.
In short, it's not really a "Joker" Movie. It's a very loosely based reimagination of the Joker but if he was a regular person who suffers from anxiety, slight schizophrenia, and depression. Like he's literally Not the Batman's Joker, he just wears make up because he had a gig as a clown for a bit in the first one. He doesn't commit any crimes, no funny punch lines, nothing. This 100% is not a DC Joker movie outside of occasional name drops of characters. They should have called it Marti the Clown or something instead... Harley Quinn isn't Harley either. She's a pointless side character, who doesn't actually love him, but gives us a few scenes with Lady Gaga as eye candy (barely).
And with all that said, they still didn't even bother to write a full complete story. It being a musical didn't bother me. There was literally just no actual story. 100% just a money grab.
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*****spoiler alert****
At the end, he cries and apologizes for the murders, admits he feels terrible, and get's stabbed to death be a fellow inmate in a prison/psychward. He literally dies. Never meets Batman. Never becomes a criminal mastermind. Nothing.