As the introduction has said for a long time:
DUMII is a multiuser adventure game set in a fantasy world. The current idea of the game is to score enough points to advance to the next level while having loads of fun! To get to the next level you will have to solve intriguing problems, kill obnoxious monsters, interact with the other players and generally figure out what you are meant to do.
DUMII is unique in the way that it is both very old (its been online since 1989), yet it has remained a simple mud without thousends of classes, millions of spells and so on. There are not a lot of choices to make about your character, you'll have to choose sex and settle on an alignment after a while, but that's all there is to it and everyone becomes the same figher/spellcaster as everyone else in the end. The players express themselves via their colourful descriptions, their unique possessions and of course via their actions, making everyone quite unique in the end.
So on one hand DUMII is quite simple. It is easy to get started even if one has never played a mud before, on the other hand DUMII can be quite hard. It expects the players to read the descriptions, think and experience the world as well as role play their character. The game play does not centre around killing monster after monster. Sure one can kill a monster if one wants and sometimes one must, but there is no experience rewards for it.