3Kingdoms rocks. It's as simple as that. The world is enormous, there are tons of quests, lots of cool guilds, and it's -not- Smaug, like some other muds we know of.
There's tons of variety, lots of cool, helpful people, a rockin' system for PK that doesn't quite count(deaths don't hurt you, and you don't use your normal guild abilities..Court World rules).
The guilds are all great, with a wide variety of powers. Jedis, Mages, Juggernauts(defensive tanks), Necromancers, Knights, Bards, Priests, Fremen(from Dune), Monks, the Breed, and Elementals.
This mud is incredibly addictive, is very well balanced, with areas for players of all level, and a good number of areas for everyone, and is by far the best mud I've ever played.