Another Takashi Miike masterpiece, less violence and more psychological terror. The ending packs a huge punch though, be prepared!
Ichi the Killer is a much more intense and doesn't come with the comforting "good guys" redeeming element that Ikebukuru West Gate Park does. However they're both very eccentric stories that feature gang violence and revolve around trying to understand who and why someone was murdered with plot twists related to mental health. They also both feature manipulative antagonists and homoerotic tension. Be warned: Ichi the Killer is fucked up.