I never played RuneScape. It looks cool but what makes it special? I read its wikipedia entry but it didn't really reveal anything.
It's special because it has been active for 25 years. There are no skill trees, instead every character has access to all 24 skills giving user's complete agency over what their character can do and has access too.
The game's rhythm is based off of a tick instead of click-and-wait. This can let skilled players abuse click rates for more xp or win PvP or high-leveled PvM fights.
The game takes a lot of time. Each skill needs over 13 million experience to get to max level, this requires significant investment for each skill, letting user's grow attached to their characters. I haven't made it this far, but there is a very rich and expansive endgame to reward the players that have made the grind to those high levels.
It can require less attention than a lot of other video games, so multi-tasking is possible and common.
I think for a lot of people it is the nostalgia around playing the same game when they were a kid.
Can you elaborate on this?
As a vaguely related example I can recommend Settled's "Nightmare mode" player-invented game mode. I don't want to spoil it ahead of time, but he fights some cool endgame content with the caveat that if he takes even a single point of damage, his account is automatically deleted.
It was the first MMO for many, so it still has a following / nostalgia factor.