This seems like a no-brainer to be shot into space. Its influence cannot be overstated, and while much of it may seem to be pedestrian if you're seeing it after seeing a slew of more recent zombie fare first, it does the genre in a genuinely intelligent and thoughtful way. Aliens would see what we're afraid of - in terms of both the monstrous and the human.
I have to cast my vote for The Babadook being shot into space not because it's the scariest of horror movies (while it's effectively creepy, I don't actually find it very scary), it shows the horror that can exist in human relationships. If an alien watched this, I'd like to think it would come away with the impression that people can have complicated, fraught, hurtful dynamics at work between them while still loving each other and committing to each other fully.