Especially those who vaguely miss the spirit of the old internet might (re)discover a lot of it in these often tight knit, yet welcoming, communities.
Tip: Stay away from strongly RP focused communities until you're not preoccupied with just thinking about navigation and the various systems anymore. Although, a lot of what makes MUDs tick should resonate strongly with anyone who wrote a program before, so it shouldn't take long to adapt.