Here is the full list of all 45 Aliens: Dark Descent achievements.
Complete Mission 02.
Secure an unconscious marine.
During a campaign, secure 5 survivors.
Destroy 4 eggs with one grenade or an RPG shot.
Kill an enemy before they detect the squad.
Kill an enemy by using an explosive barrel.
Complete Mission 01.
During a campaign, kill 100 Xenomorphs.
Prevent a marine from being Abducted.
Save a marine from dying of Bleeding.
Remove a Trait from a marine.
Kill every Alien of a Massive Onslaught.
Finish the Prologue.
Complete Mission 03.
Complete Mission 04.
Complete Mission 05.
Complete Mission 06.
Complete Mission 07.
Complete Mission 08.
Complete Mission 09.
Complete Mission 10.
Complete Mission 11.
Complete Mission 12.
Unlock the APC.
Finish the game on Medium.
Finish the game on Hard.
Finish the game on Nightmare.
Finish the game on "No One Can Hear Them Scream" mode.
Kill every Queen during a campaign.
Advance a Sergeant to level 10.
Advance a Gunner to level 10.
Advance a Medic to level 10.
Advance a Tecker to level 10.
Advance a Recon to level 10.
During a campaign, advance each Marine Class to level 10.
Lure a Queen into a Mine.
Save a Marine from being incubated.
Keep all of your marines alive during a campaign.
Gather all datapads.
Have one Sentry kill at least 10 aliens.
Make the ARC/APC run over an enemy.
In any mission, complete at least one objective with only one marine in the squad.
During a campaign, unlock every Xeno Tech.
During a campaign, unlock every weapons.
Have a marine with at least 2 Prostheses.