Sonny Boy is unique and special. If I had to categorize it, to enable people to get an idea, I would say that it belongs to that mysterious family, not entirely understandable, of anime where one could put Serial Experiments Lain or Evangelion (or Nolan's Inception, if we were to go to the movies, for its originality, photography and bewilderment).
It is hard for me to think, after the experience, that this series can leave anyone indifferent. While it is true that in its course I did not get to understand everything, the series corroded me, disturbing my mind and body until an existentialist doubt took hold of me, an uneasiness that was progressing until it materialized in a slight pressure in the chest. There are several moments in which everything that happens disturbs your being and reason to the sound of reflections that you can hardly get rid of or respond to the moment. The merit of inducing such sensations seems to me commendable. The visual and narrative means used tell the story in such an effective and attractive way...
It is worth noting that Sonny Boy is a visual spectacle with wonderful shots worthy of competing for the award for best anime cinematography (in my opinion of all time), if there is such a category as there is in cinema.
I recommend watching it when you are ready to be solely focused on it.