Outer Wilds and later its DLC: Echoes of the Eye,
At the end of the vanilla game, when I found every piece of knowledge there is, every piece of dialogue between characters dead and alive alike, connected the dots to the solution to opening the door to an ending that remained the final main mystery; I just didn't want to finish it so completely. I may have not known the answer to the question that the ending was about to answer, but I was sure of two things:
I wanted to go through the whole star system one last time before the final answer, and yet I couldn't even do that as I realized this final voyage would only wake feelings of nostalgia, not the exploration and mystery solving that I most certainly craved. As a result, I just stopped playing for a few hours, just thinking about all the question and answers in my mind before I embarked thorough the final door.
Then the DLC got published. At the end of the DLC, after the exploration of environments previously unknown, solving puzzles that were even better than the original ones, learning of mysteries that I didn't even realize were mysteries in the vanilla, all the parts clicking so thoroughly... Made the vanilla and the DLC together better than the sum of their parts. After the reveal of the final DLC mystery, I just had to wait for the time to take me just thinking over what was revealed, instead of following what the game kindly suggested I do at that point.
This game was an incredible find for me and became one of my favourites the moment I realized the sea of mysteries before me. Then, with the addition of the Echoes of the Eye, rose to be the definitive number one with their intrinsic power alone.
To think I found it while looking for games with as rewarding explorations as Subnautica, and it's unexpectedly perfect delivery of this wish and more with such completeness. I am eagerly looking forward to as lucky finds as this in my life going forward.