Martin McDonagh is known for his violent and darkly comedic writing in the theatre. He brings his savviness of wit to this film, along with the violence. McDonagh is a man who is capable of making you laugh in one beat, cringe in the next, feel deeply in the following and finish you off by making your stomach turn with a gory image. The writer, director has a unique way of showing the human condition through the lens of the most horrific circumstances one could be in.
This violence & gore brings a hyper-sensitivity to the screen in a way that translates far different than most filmmakers are capable of achieving. How he does it? It's hard to say, but his use of violence isn't for affect, rather it's to heighten the gravitas of a character's reality, and it is directly in line with their actions. Take for instance Harry killing himself. He's just blown the head off of Jimmy, who he believes to be a child. A headless body lies near Ray, and Harry looks it over. It's a gory reality, but one that causes Harry to either stand on his principles or violate them. This is what I mean by the gore connecting to the motivations of the character. Without this, McDonagh would be a terrific horror genre filmmaker. But with it he has carved out a unique one-of-a-kind style that lands in a way that's always fresh.
This puts him in a unique category of current filmmakers whose style is distinct enough that audiences known their work, such as Quentin Tarantino, Christopher Nolan and Taika Waititi to name just a few.