What are your thoughts about John's war PTSD? In the show it's almost not talked about at all while Arthur's and Tommy's PTSD is an extremely important element for their characters.
I've touched on it a bit here, but I think most of his PTSD is looked over. It's mentioned or implied that he's struggling when he's found with Tommy's opium pipe. He tends to blame things on season 1 as not having a wife, which, I would not be surprised if Esme is his confidant about all his war issues. When Ada visits, Esme tells her that John shit himself while in the noose, and John's unhappy she shared it, which is understandable, but I think it shows that he doesn't like his family to know when he's weak.
As the seasons go on, you see it in how he reacts when Tommy starts leaving the brothers out of things. "Be a toy soldier and kill your teacher, John!" He doesn't like taking orders without a reason, and it probably has to do with being a soldier in the war. He doesn't like feeling out of control.
He also has anger issues. You see it when he fights at Grace's wedding, and when he fights Lizzie's boyfriend, or at the races. I think his aggression is part of it. It's an outlet.
So yeah, they don't explicitly touch on it in the show, but I think how he reacts to his PTSD is still shown in how he behaves, it's just different than Arthur and Tommy.