I first started playing SK (Shattered Kingdoms) about five years ago. From the first time I played, I was amazed at how large and immersive the game was. SK has a huge map that offers several nations, islands and countless hidden areas. SK also boasts a rich history that has been majorly impacted by past characters. The possibilities for roleplay are staggering, ranging from "fountain RP" to acts that may forever alter the realm and make your character's name legendary.
The roleplay is what keeps me in the game, but an ever important tool of that roleplay at times is the unrestricted player killing. While player killing is unrestricted, it still remains a tool for RP, and it is expected that there is a strong in character reason for your character to kill another. As for mechanics, I am rather fond of the fighting system that the implementor has devised.
After playing this MUD, I haven't been able to find any other that keeps my interest, the maps, history, the mechanics, the population...it's what keeps makes it home for me.