This is the last part of the real Halloween franchise. After this the the Myers saga was resurrected Frankenstein style.
Like Halloween II, though this was not directed by Carpenter, Halloween III has his signature stamped all over it. Along with a story co-written with Nigel Neale (he disowned it) and having a hand in the production, Carpenter also contributed the music. One of the, rarely commented on things about, Carpenters early films is that the soundtracks stamp an authorship on them just as strongly as the directing style, writing and editing. Though there were lots of similar electonic scores in that era, Carpenters's are still instantly identifiable because they have a propulsive insistant rock drive that gives the films movement even when nothing at all his happening. Somone walks across a street and ting, ting,ting, ting, ting....there's a sense of speed. A shot of an empty corridor and its ding, did-ding,did-ding ... filled with menace. The music alters what you see in the same way Enio Morocone's music dominates Sergio Leone's films or Mark Mothersbaugh's (Devo) gives Wes Anderson films an identity.
The other thing that ties Season of the Witch to Halloween (I and II) is Dean Cundy's camera work, which was always stunning. These are the elements that, to me, make Season of the Witch the last real entry in the series and the other films simply ok to poor studio cash ins. The story is good too and Tom Atkins, looking pemanently hungover, is always great value.