Browser games aren't so two-dimensional anymore. There is a huge amount of potential in them. By today's standards Runescape is very far behind. In optimization and appearance. However - the look is a bit, I believe unintentionally, stylized giving it longevity.
An okay example would be the
Battlestar Galactica Online game. Its an awful game but tens years ago, when Runescape came out, if you had asked someone if something that looked like that was
realistically possible in a browser the answer would of been a resounding no.