Different kinds of armors and different types of alien attacks.

Armor Types:
Security Armor = Reduces scratches and bites
Green Armor = Reduces acid/aoe attacks
Black and Green Armor (Restricted to low chance of discovery upon derelict exploration) = Reduces all damage types by 25%

Attack Types:
Acid spit and pooled traps
Flame attack type? Derelict hazards? Booms booms and screams?

Alien Types:
An Elite Alien brandishing a lazer weapon (hard opponent).
Queen? Maybe she's constrained to one room but spawns aliens in intervals?
Chest busters? Would be cool to watch someone's ship divulge to chaos because an undetected chest buster was in a crew member during a twitch stream. It could hide in the vents and if a crew member falls victim it could create distrust among crew members like the film Thing.
Boomer (L4D) Alien?

I think having an ammo count for the guns would be cool, too. Also a really hardcore randomly generated mode would be fantastic!