A bit late to the party, I know!
While I know there are some threads technically discussing this, I wanted to make one a bit more focused on not just the big things in the last level, but some of the small things thorough the whole game too. So with that said:
Quote-Isolation is referenced multiple times
-Novels and RPG are referenced multiple times
-Colony uprisings
-Cults being built around the Aliens (with the Aliens embracing the easy prey instead of just senselessly slaughtering them)
-Xenomorphs are still not known through the galaxy, with WY being the only ones to know about them to some extent
-Before the miners that found it died, the Space Jockey City was the first time humanity had ever found evidence of intelligent life, meaning the find was done before the Arcturians were found(which fits, as Dark Descent takes place in 2198 and the Arcturians were first found in the late 1900s, at the very least a bit before Aliens, so 20ish years before DD.)
-The Hive Mind, it's range and the fact that, with enough tampering, it can be accessed by humans.
-Aliens being, once again, implied to be smart in an almost human level
-Aliens changing the size of ovomorphs/facehuggers to fit different hosts
-Space Jockeys and Engineers not being the same things
-The game ends with the OTAGO having kind of a happy ending, with enough proof to show that not only do the Aliens exist, but WY has tried weird shit with, which can lead almost seamlessly into Aliens Fireteam Elite.
-WY Commando design uses the same design as the one featured in Fireteam Elite, further suggesting the connection between the 2 of them.
And probably much more that I missed!
