During one of the final moments of “Joker: Folie a Deux,” the anticipated sequel that hit theaters this weekend, Joaquin Phoenix begs a character to “please stop singing.” As it turns out, it’s quite likely that most audiences thought that very thing long before they got to that moment in Todd Phillips’ new film. However, that the film is a musical and that the filmmaker has not been afraid to experiment on a grand scale are the most interesting and admirable qualities of this production. The problem is that this and the monumental talent on display fails to mesh and the existence of this cinematic exercise that wants to mix art, commerce, depression, violence and musical.