I used to play Runescape. It's very addictive and complex, hundreds of things to do. If you get bored doing one thing you go and do another. The reason why people seem to not take it seriously is it's graphics... but for a free internet browser game they're fine. If they turned the game into a CD-Rom which you buy with better graphics it would be more popular that World Of Warcraft for sure.

Another good thing about it is they always update it. I've heard that they've updated the graphics for members (membership has more than double the features at about £3 a month, not that free2play feels like a demo, it's still a huge game), and now they're not too bad (they're not PS3 quality but oh well :P).