ALIEN is a slasher in sci-fi clothing. It follows the conventions of HALLOWEEN to a fine point. We get the Final Girl, the obligatory cat scares, the endless amount of characters wandering off to meet their demise, the long tracking shots and the its-not-dead-yet reveal at the end. Although it is set in space, its story is more slasher than anything else. ALIENS though, I would argue, is far more action and far less horror. Rather than stalking and slashing, ALIENS treats the whole thing as if it were a military war, giving it much more of an action vibe. It's much more bloated and adventurous than the tightly knit original, and the Final Girl archetype doesn't really apply to it either. I'd say both ALIEN and THE THING are horrific enough and both modelled enough on slasher films that they could both be considered as horror films.