First of all, let it be said that there's no way the filmmakers honestly believed that the fourth movie in the series, subtitled The Final Chapter was in fact the final chapter. In fact, if anything, the subtitle should have been A New Beginning, since the ending of the movie so clearly establishes a supernatural exit strategy for a villain that should otherwise be dead.
That aside, this movie is a pretty good follow-up to the movie that preceded it. I've already written about how the first film particularly is unlike any of the rest of the series, and for that reason, the third movie truly was the start of the Friday the 13th we all know today. Not insignificantly, of course, it marked the introduction of the famous hockey mask, which is carried over into this film (as a title graphic, even). Other themes are inherited, too. The teens grow ever more annoying, Jason is freed from constraints of life and death, and, as far as I can tell, physics. This is Friday the 13th, unapologetically larger-than-life.
In this movie, Jason terrorizes two households, one a small family of a mother, daughter, and young son, and the other rented to a group of randy teens out to party. It was, I imagine, a calculated hedged bet: pit Jason against the holiest of innocents, the American family, and a group of rowdy kids. You worship and yet revile one and hate and yet envy the other. What better way to exorcise these feelings than by watching Jason, the bringer of indifferent and absolute justice, kill them both?
And that's mostly how the movie goes. Jason kills as many people as he possibly can. I'm not sure whether it was written this way or whether it was accentuated in the edit, but it does seem that Jason gets from one house to the other in record time. In fact, if I didn't know better, it seems he's literally in both places at once, to the point that it seems for a while that it could be part of the plot of the film that there are actually two killers and not just the one. Admittedly, sometimes what the viewer thinks is Jason could have been a fake music cue, but by my reckoning it seems that Jason must have had help, if not from a person then from the powers governing space and time.
At the end of the previous movie, Jason died with an axe planted in his forehead. He was definitely dead, and this movie opens the very evening of the previous movie's ending, with police swarming the farm, and ambulances arriving for cleanup duty. Jason is taken to hospital and, but for an inattentive coroner, would have been pronounced dead, until he manages to rise inexplicably from the dead to kill again.
Without question, Jason has been transfigured into a supernatural force. He is beyond death now, and essentially inhuman. He's a monster.
The beautiful thing about monsters is that they remove all questions of humanity from the equation of battle. With monsters, you don't ask for motive, and you aren't required to feel pity. And that's what you want in a Friday the 13th movie.
It's exactly what you get from this movie. And it's contagious, both for you as a viewer, and for little boys eager to grow up to be monsters, in the movie. In fact, while the series truly found its monster in the previous film, it finds its heroic archetype in this one. There is no single hero in Friday the 13th, but with Tommy the dye is cast for a sort of Chosen One. The one person who comes along, every two films or so, who can survive Jason and, temporarily at least, defeat him.
It's as satisfying an archetype as any D&D hero or comic book avenger. We relish in the victory, knowing full well, deep down, that the monster is going to return even after a story subtitled The Final Chapter.