I read Halsey's book shortly after he retired and although it was clear he was going to be controversial in order to sell copies and he did come across as having a huge chip on his shoulder.
He felt there was a big (social) divide between the likes of himself and the 'chosen' few that were destined for big things and could get away with anything, in particular he had no time for Graham Poll ( have to agree with him there!).
He kept stressing that he was the man that they looked to for the tough games where there was likely to be confrontation. He was never going to be a 'yes' man and he was bitter about his perceived treatment and this outburst against PGMOL comes as no surprise, it was only a matter of timing. I don't think this will be the last time he hear of him and things that go on in the background.
He did have a rough time to say the least with cancer and it took a lot of mental strength to back after it.