Anecdote: Small client-side scripts for Starseige:Tribes were probably important in leading me to software development as a career.
There's a certain poignant sadness to how that era of relatively open modification has vanished--no longer can you customize a crosshair simply by replacing a bitmap file.
The most influential video game in my life of learning was probably Robot Odyssey.
https://robotodyssey.online
https://en.m.wikipedia.org/wiki/Robot_Odyssey