MUDs are generally usually either role-playing based (full of people pretending to be medieval and shit) or stats-based (more like a real video game, where you trick out your character with the best equipment and team up to kill the hardest monsters and solve the puzzles, etc.)
the one i was on was more stats-based, but it had a sizable amount of people trying to role-play. the end result was that the stats players preyed on the roleplayers and continually killed them and stole their equipment, saying things like "hey fucktard gimme your 5dam zeus sword or i'm going to turn you into hamburger" while the rpers were like "What is this odd style of speech thou hast, stranger?"