Prince of Darkness. Carpenter even appears on the DVD to talk about his love for the movie.
Watching it for the first time, I see why it appeals to Carpenter. It's apocalyptic sci-fi horror, it's dark, and it's cynical, like Prince of Darkness and The Thing. It mixes subtle mystery and tension with (for the time) graphic shocks.
Based on the work by Nigel Kneale (this was first done as a serialized TV broadcast on the BBC and highly acclaimed, but that version is sadly mostly lost) and directed by Val Guest, The Quatermass Experiment is about an astronaut who returns to Earth, but he's not himself anymore. He ventured beyond the veil human boundaries and encounter something beyond our comprehension. I love it when movies aim for that kind of cosmic terror.
Victor Carroon (Richard Wordsworth) was one of three astronauts launched into space in a rocket by Professor Bernard Quatermass (Brian Donlevy), but he's the only one found on board when the rocket crashes on a farm. When he's dragged free, all Victor can say is "Help me," before slipping into more-or-less a catatonic state. Before long, it becomes apparent to Quatermass, Scotland Yard Inspector Lomax (Jack Warner), and others that something inhuman has taken over Victor, and it threatens the entire world.
This version of The Quatermass Xperiment is a condensed version of the six-part TV version, and it runs a little over 80 minutes. As a result, the characters and some of the plot developments feel a little undercooked, but the film is packed with ahead-of-its-time science fiction concepts. If you're familiar with the works of John Carpenter, The Fly, Invasion of the Body Snatchers, Lifeforce, and Species, you'll recognize such tropes as the alien that looks human, the horror of a body revolting and transforming into something unrecognizable, the monster that drains the life out of its victims, and the shapeshifting alien.
The movie also generates some pathos for Victor. In a mostly wordless performance, Wordsworth is rather creepy when he eyes people, but you do get a sense of the frightened man trapped and resisting this alien presence in his own body. His arm is the first part to mutate, and he hides it in his coat pocket, and we anticipate what's going to happen and what it will look like when he reveals it. In a scene reminiscent of the one in Frankenstein, Victor encounters a little girl, and you know he's fighting the urge to harm her.
It does lead to a great closing shot. After the monster is vanquished, Quatermass strides down a dark street, declaring he must begin his work again; he's practically inviting another alien menace. We defeated this threat, but who knows what else might show up on Earth?