I have been playing on the Discworld MUD for about three years now, and I must say that it's been a lovely, wonderful experience, and that I have no plans of quitting anytime soon.
Discworld MUD is based on the hugely successful and insanely popular Discworld series by author Terry Pratchett. If you haven't read the books already, I strongly suggest you do.
Being based on the books (which themselves have a rather open-ended storyline), the Discworld MUD has an overarching sense of unity and trueness of atmosphere, while at the same time freeing the characters to do pretty much what they want to do.
And what a large number of actions they have to choose from!
Players can do the standard MUD thing, getting xp, advancing skills, and just being all-round uber. If that is the path you wish to follow, know that Discworld boasts of a very complex combat system with very realistic weapons, (as well as the rather outlandish talking sword, or the Ukelele of Pain). You can ambush opponents, yell at them to frighten them, prepare extra powerful attacks that hit for far more damage, feint at them, and trip or shove them to the ground. If you are magically inclined, you can cast a huge variety of spells to damage them and protect you from harm, while priests can ask their God to protect them from harm and smite the unbelievers.
If simple combat power is not your goal, and you appreciate a varied interesting environment to explore, the Discworld features over a million (yes, a MILLION) rooms to explore. Have fun seeing the locations from the books in real life, as it were. The game features days and nights, as well as seasons and the weather. On a snowy winter's night, for example, you'd better wrap up warm, or you might catch a cold.
The politics in the game can get deep and sinister. Many Guilds you can join are run by players themselves, and the 2 cities of Ankh-Morpork and Djelibeybi boast of player councils, where players who are magistrates make the rules for the city. In case of disputes where players are unable to achieve an amicable settlement, there is always the Assassins' Guild, where for a small fee you can make sure someone... is annulled tastefully.
You can own a shop, own a house, write for a newspaper, write plays, become a professional musician, cater for parties, host parties. You can get married, start a family, start a club, hire out your services to other players... well, the list is almost endless, and as soon as you can think of a new one, you can get the creators (theyre like the wizards/Gods/Admin in other Muds) to code it in for you :)
On top of all this, the social aspect of the game is what will keep you coming back for more. With more than a hundred players usually logged on at once (sometimes peaking at two hundred), there is no shortage of social interaction. The people are really nice, (well, most of them are), the creators are approachable, and very soon you will feel like your guild is your new home.
So come come all, to discworld.atuin.net port 4242.
Try and ignore the cabbages, frogs and wombles though, after 3 years of Mudding, even I still don't know what theyre really about.