I must say that I personally hate Materia Magicka, although if I had never played any other muds, it would be a wonderful one. The reason I hate it, is that pretty much every other MUD (not MOOs or Mushes) seems to derive its exact skills/classes/so on.
That said, if your looking to expel some time playing MUDs, I suggest either LegendMud or Lensmoor (neither of these which I have played in the last year, so I can't tell you how dense or sparsely populated they have become.) Legendmud because it has a really cool RP-playerbase, and is just a blast (especially the magic system). Lensmoor because it has crafting and thats always a plus for me, plus its just fun to dink around with a classless system.
(By the way, LegendMud has 'three' (or maybe more now), 'time' areas, so you travel into the future, or back into time, or what have you. But it also forces you to really play and read it, because if you walk into an area without first looking at that area, you could easily come across an insta-death zone, which all your equipment is thusly gone forever. That said, its really, really fun)
Kayla
Edit: While I do hate MAteria Magica, it is fun (albeit unsophisticated), and the seemingly endless amounts of muds derived from it is probably because of that. So give it a shot, take a twirl, have a fun roundabout.
[ February 11, 2008: Message edited by: Kayla ]