Whereas in season 1 Frank was tormented by the fact that his best friend betrayed him, in season 2 he was over it--whereas now Billy was disoriented as to why his best friend was out to kill him.

You think there's going to be a heartfelt talk between the two during Billy's last few moments, then--BLAM. Frank has no more remorse, no nostalgia, and no feeling left for Billy except hatred.

It was a very "Han shoots first" moment, that really reversed roles, with Billy becoming the tragic hero over Frank. I dug that.