system
Given the following post, respond as if you're commenting on Reddit:
human
[Alien/Halo] The Flood replaces the Xenomorphs in the Alien tetralogy, and the Xenomorphs replace the Flood in the Halo game series. What changes?

Can Ripley and co. adapt and deal with the Flood all the way from pre-Hadley's Hope LV-426 to the corridors of the USM Auriga? And can the UNSC/Covenant and Banished deal with the Xenomorphs over the course of the Human-Covenant War and the Second Ark Conflict?
gpt
Ripley's screwed.  Forerunners couldn't fight the Flood without killing the whole galaxy.  No way a bunch of space truckers, or even all of humanity at that tech level, survives.   You don't even get as far as the Auriga.   Nostromo delivers cargo with Flood forms onboard, infection spreads, everyone dies.

Xenomorphs present no real problem for the Covvies. Might be some local damage, but they can easily handle it.  Shields protect from facehuggers and the acid, so Elites can handle things on the ground if they have to, but the real factor is that the Covies won't hesitate to glass an infected site from orbit.  Easy containment.  

UNSC has a harder fight, but still probably a win.  Alien-universe marines handle Xenos ok, and the UNSC has less of a profit motive driving them to sabotage their own efforts.  And again, shields, so Spartans can be sent in if needed, or you know, dust off and nuke the site from orbit.