One is that it's is VERY well run. It has a variety of areas while still maintaining a continuous historyline. Finally, the people themselves make AA the greatest. They have pride in their mud and what they've accomplished and built here, and it will perservere for a long time to come because of it. Let's see, where to start, I guess the Internet itself is a good place.
Muds are the islands that make the internet fun to swim in.
Now, AA in particular. I first discovered mudding through a friend at Uni, and although I'd never tried anything like it before I must admit I was tempted. Not because it was 'cool' or because of peer group pressure. I felt I was 'mature' enough to cope with the whole aspect of it. I found the Mad Prisoner.