Realms of Despair has a rich and varied player base, has a lot of people online at any given time, and has immortals who are very good, responsive, and constantly changing the realms to make it a dynamic place to spend your time. The classes are being developed as are new areas. I have been with the realms for quite a few years now, and have seen it grow into a better community who enjoy both RP and PK. It has quests with which many things can be earnt and lots of fun can be had.
Realms of despair is good for new mudders and experienced mudders alike, it has lots of runs and allows limited multiplay in case your friends are not online when you need to get an item. However, there are many channels which can be used and it is a good place to meet new friends.
Overall RoD is one of the best MUDs I have played, rich in content and variety with areas with puzzles as well as mob kills. A wonderful place to spend your spare time!