www.globalmuonline.com
I haven't played it yet, but from what I've seen on the screenshots and the fact that it actually has really good 3D graphics (unlike some other games... *cough* RUNESCAPE *cough) and is basically free* I can't wait for it to finish downlaoding.
*There is a pay service whereas you can have better customer support and access to special events and servers where there is less lag, but there isn't anything ultrabonus you can get from subscribing, such as runescape.
Btw, I don't think the world's very big, but give it some time to develop, it isn't even a week old yet.