I've been playing Arcane Ages (previously TeraMUD) seemingly forever and still have not explored every area, nor played every class. In the time that I've been playing the mud has grown significantly, in areas, players, items, and story. I've tried other MUDs, and found that I couldn't get into them as deeply, though TeraMUD does have an emphasis on hack-and-slash gameplay. The sheer number of ways one can approach the game is staggering, and in the end simply fun.

Arcane Ages is also very newbie-friendly. Almost all players are ready to help someone new learn the game, and the help system is very comprehensive and complete. There are plenty of warnings and areas for newbies to use to learn the game, before continuing on to more challenging goals.

The clan system Arcane Ages deserves a mention as well. Any player can found a clan, and with enough gold, can have a clanhouse and clan gear made for them by the gods. Both pacifist and warring clans are available, depending on the play-style each person prefers. Clans first and foremost foster camaraderie among players, and provide help when it is needed.

The mud is by no means done being developed, many projects are constantly in the works, and new content always coming online. While less populated than larger muds (probably won't see 100+ players on at once), the staff of immortals and the player base are very dedicated, and a great bunch of people. With tons of classes (and combinations), races, skills/spells, and areas, I believe Arcane Ages to be one of the best MUDs around.