[Anaiah]

I think you might like Armageddon. I spent a little over a year on staff there. It's a very enjoyable game and fits most, if not all, of the requirements you posted looking for, though it moves more quickly than a MUSH, using the emote system, rather than a pose command.

I've tried many other RPI's and RP-enforced muds, but that one is the only one that has ever kept me hooked. It has made me laugh for joy and cry so hard I could not see the screen before. It is a wonderful place, if you're looking for deeply immersive roleplay in levelless game with a cap on PC ranks, an active staff, enforced RP, limited to the room OOC command, and so forth. It also has permadeath, though, so you will likely die fairly quickly if you leave the relative safety of a city without getting an idea what the world is about, but all in all, I believe it is a good fit to the desires you expressed having for a new mud.