I know a lot of people totally disagree with this but AD&D/OD&D/BECMI was more you playing a game, later on it became more you playing a character. Emphasis moved from the player and his choices and more to numbers on the sheet. The DM wasn't trying to challenge the players with traps and puzzles as much as she was challenging the skills and abilities on the sheet. I used to always hear complaints of "but player X at my table is a real idiot and that hinders him when he tries to play a smart PC..." Or "player Y is nearly catatonic and we need skills and more systems so she can play a charismatic character!". Emphasis moved from the adventure environment to the "ding" of level advancement so build tweaking could commence. And to help this advancement became quicker and quicker. You didn't do multiple modules per level, you did multiple levels per module.
I never thought of it that way, but there is truth to that.
In 1e, the characters are so minimalist they are defined by their experiences, rather than their stats.
Three memorable characters that I played in 1e are, an Illusionist, a Druid, and a multiclass Magic-User/Fighter/Thief. When I think about them now, what I remember is the things that they did: vivid encounters, their adventures, yet also the unique spells that they researched.
Spell research is a kind of mix of adventure and stats. But it is the adventure, the personal invention that is memorable. The creativity and imagination.
As part of world building, the characters had specific relationships to other characters. Especially, new characters tended to be the children of retired characters. These relationships were mostly ‘off camera’, rather than being acted out. The relationships were setting details, from which the adventure commenced.