Getting to the top of the mountain in Celeste. It may not be the hardest challenge in the game (screw you Farewell), but just arriving there with the soundtrack swelling felt so good.

Completing the golden path in Tunic.

Any number of silly things in FFXI that at the time probably felt immensely important.

I played it and Blue Shift way back when. I don’t have a lot of specific memories of the levels or story. At the time I was just happy to have more Half-Life to play, and I enjoyed it.