When the big brother dies in Brothers: A Tale of Two Sons. The game is short, but does a great job of getting you emotionally attached to these brothers. Even through the controls, you control both brothers at once with each getting half of your controller. When he dies, it also essentially kills half of your controller. I found myself trying to move the brothers together as I have for the rest of the game.
Subnautica of course was a banger, but recently I’ve been insanely addicted to Icarus. The mission oriented gameplay makes the survival gameplay less tedious even though I’m doing similar stuff. You drop down, figure out what you need to complete the mission, set up and get the mission done, then get out. You have meta progression to make missions quicker to work through and you have a levelling system to further impact your strength. Just a super satisfying loop to me.