a good bit more "casual" but I think toontown was the first online game I played besides neopets? it was incredibly frustrating because of how fuckin long it took to load anything + it was impossible to get anything cool without spending irl money
I played runescape too but I hated it because it was so boring looking and you had to kill animals
there was also this game called "spineworld" which was this mmo/rpg with really awesome pixel graphics and cool locations but it got shut down