A spectacular deep dive into Arthur and Harleen’s insanity. Anyone who has given this movie a bad review simply does not understand it. Review bombs are inflicted by an entitled fan base that has become accustomed to repetitive DC film tropes, many of which simply have no artistic bone.
This film is artistic, and musical features are present simply to demonstrate the mental instability of the two characters - it is therefore not a musical in the traditional sense.
Go see the film, approach it with an open mind, know that it is an artistic experience that delves into the human psyche. It is a devastatingly sad movie that has deserved much higher praise.