Recently, a friend and I were discussing old times, before the graphics intensive games of today. I mentioned that I hadn't played muds in years, as I got bored with all the running around killing things with no social interaction. He recommended Discworld to me, after affirming I'd read a couple of Pratchet's novels. Although they arn't neccessay, its a blast to see all te book series laid out so nicely. Two things in my mind emerge as distinguishing this mud from the masses. First, the people on there are willing to take time and resources to help any newbie. Second, the system is incredible detailed in description and has pretty good parsing. Ok - the third (I know I said two, but there's lots...) is the classless, skill driven system.
I strongly recommend this mud to anyone that wants a good mix of fighting, conversation, and friendly envirenment.