This climax to the Phantasm series claims to "finally explain the origin of the Tall Man," and actually does. Sort of. Mike, the nemesis of the Tall Man, spends most of the movie on his own, learning about the new powers he acquired in the last movie and also learning more about the Tall Man. We learn that the Tall Man used to be a hospitable southern coroner, who just got too interested in the line between life and death for his own good. After building a dimensional gate, he goes in and comes out as... the Tall Man. And that's all we find out.
Reggie is trying to track down Mike, and yet again tries unsuccessfully to have sex with a woman he meets on the way. You have to give Reggie credit for sticking through this quest against the Tall Man. You can tell that he's just a regular schmoe that got caught up in it, and in a tribute to his humble origins, at one point as he's gearing up for battle, he puts on his old ice cream vendor outfit.
One interesting thing in this movie is that it becomes apparent that The Tall Man is striking all over America. Small towns everywhere are deserted as the influence of The Tall Man spreads, so the series in general seems to be heading toward some kind of apocalypse.
This movie continues in the series tradition of low budget, and you can count the speaking cast members on one hand. A good part of the movie is "flashbacks", which are actually just clips from Phantasm that were originally cut. These clips do help the movie along somewhat, tying the whole series together, but it still comes off as a cheap way to make the film feature length.
The Tall Man makes several vague references in this movie to some grand plan for which he needed Mike alive all along, but we never get to see what this plan is. The movie still leaves more questions unanswered than I would like, and the ending is virtually begging for a sequel. Apparently there is one in the works, with Bruce Campbell playing a part.