Here is the full list of all 27 Halfway achievements. It takes around 15-20 hours to unlock all of the achievements on Windows.
Complete an optional mission.
Kill 20 enemies.
Kill two enemies in one turn with the same character.
Loot and empty 10 containers.
Samuel Lankford joins your team.
Kill an enemy at full health with a single ranged attack.
Kill Johannsen, or what's left of him.
Linda Carter joins your team.
Complete the game's main story.
Kill four or more enemies in one turn with all characters.
Kill 100 enemies.
Kill 500 enemies.
Carefully listen to conversations without interrupting them.
Have the backpack at full capacity with at least three characters.
Have the team storage at full capacity.
Complete all optional missions in one single play-through (progress resets when starting a new game).
Find the hidden cake.
Josh Connor joins your team.
Dr. Schaffer joins your team.
Gina Nia joins your team.
Subject 13 joins your team.
Jenna Wallace joins your team.
Have five characters join your team.
Have all characters join your team.
Loot and empty 50 containers.
Survive a fight with only one of at least three character fit for action.
Recycle loot to gain 1000 energy.