I think without Joaquin's performance the whole thing really falls apart. No one else really had a character arc and so much of it is his perspective that without his performance it doesn't have anything to really stand on.
Isn't the whole thing a character study on joker? It wouldn't work at all without Joaquin. It would be like asking if a burrito is good if you remove all the filling. It's not really a burrito at that point.
I think it did a great job of leaving you conflicted about the character. Do we pity the joker who seems to suffer from mental illness and some sort of ptsd, does this excuse the actions of the character?
I think the whole move was just a made up store that joker was telling to the psych in arkham at the end that he killed, just like the comics there are so many joker origins that you dont know what is true and what isn't