Let's begin with his very first directorial effort, a short called Xenogenesis.
There isn't much of a plot to the main action of this piece; it's more of a special effects demo of sorts. In a futuristic environment, a young man tries to survive an attack from a giant robot, and his lady friend fights the robot with a large mechanical spider-like vehicle. For a minimal budget, the effects look very good. The integration of the live action with the stop-motion robot effects are almost seamless.
The film exists as a kind of in medias res tale as part of a larger story we never get. In fact, it ends on a literal cliffhanger, feeling like an old movie serial or a television episode (we get an executive producer credit after the blackout). It's sort of a shame we don't get more because the backstory is engaging. The movie opens with expositional narration over illustrations telling us of an android and the woman he loves. The title Xenogenesis bears no connection to the rest of the film, but it would be very interesting to know what sort of story Cameron had in mind for the broader picture. Watching this opening sequence, we realize what a fabulous illustrator and painter Cameron is as well. He spent years in the model department and various other levels of production design for Roger Corman's group. His concept art is really lovely.
Despite some of the lame acting and the lacking plot, one can see the seeds of other Cameron films on display. The expository teaser mentions a great cataclysm prefiguring Terminator' future war, as well as the cyborg element. The production design is stark and interesting. The spider robot controlled by the girl is an obvious precursor to the Ripley-in-the-loader scene from Aliens, and also slightly calls to mind the sequence from The Abyss where Bud is outside Coffey's sub and it is being rammed by the other sub.
Ultimately, it's a tease of the effects-laden career that Cameron will have as a director. I wish that one day he might return to some of these elements, and show us what sort of story he had in mind, because the action on screen pales to the story illustrated beforehand. Also, I've only seen this film online in a rough transfer; I wonder what the final text says after the credits, because it is impossible to make out clearly. Xenogenesis is not much of a movie, it's not even much of a real short, but it's a strong effects demo and a curiosity that should be sought out by Cameron fans.