There really isn't much to the plot here... some sorority girls, alone on Christmas Eve with their house mother start getting mutilated, one by one, because their sorority house is the same home of psychotic killer, Billy, who murdered his mother and step-father years 10 years earlier. Apparently, after the mass murders, the home was turned into a sorority. That psychotic killer, breaks out of the mental hospital, and heads straight for his childhood home - hence the murders.
There really wasn't anything too special about Black Christmas. The back story on the killer is pretty disturbing (anything involving rape & incest kind of transcends horror for me and just enters the realm of tragic lifetime movies). The story moves along slowly and there's no surprise ending or anything. There are only two redeeming qualities here: one - the psychotic killer is afflicted with a condition giving him yellow skin, which makes for one creepy villain(that's worth a half star).
Two - in a slasher film taking place in a sorority house, there is not one nude scene. The closest we get is a nude back. When it gets more lurid on Fox network television, you know you've got something pretty tame. Now, I'm not saying that no nudity is a redeeming quality, it's just that I respect that this slasher film in the typical "sorority/girl's camp" setting, they avoided the temptation to turn it into soft core porn. Disappointing - sort of, but also redeeming.