Realms of Despair is easily one of the best (if not the best one) hack and slash MUD that there is. It's also pretty much the only SMAUG MUD that has at least somewhat active playerkilling community, and has a small roleplaying group as well.
The MUD widely practices multiplaying - peaceful players are allowed to log up to 8 characters at one time, and own any amount of chars (older players have literally dozens of chars), which leaves a lot of room for improvement; managing your own "army" can be a lot of fun in itself; watching this "army" grow and strengthen can be pretty interesting as well. This doesn't mean everyone is playing by themselves of course - most stronger mobs will require cooperation from fairly large groups of players, regardless from if they are "multiable" or not.
Cooperation and communication between players is very much encouraged in general; numerous guilds, orders, and councils exist, enough for players with any kind of tastes and styles of play - from diabolic Baali and secretive, elitist Inconnu to rugged Dragonslayers and magical Arcanes.
There are many events such as yearly Inter Guild Pkill, monthly Inter Guild and Inter Order Quests, regular immortal-run quests, trivias, arena pkills, etc. There are also many areas, each with their own secrets and puzzles, as well as monsters and treasures to discover; many still are being built and put into the game on a regular basis. Realms of Despair has an open build port as well, for anyone interested in creating an area of their own.
Immortals are numerous and generally approachable for any issues or ideas, and anyone is always welcome to submit any suggestions or concerns about the game, without a doubt that they shall be heard.
either way, enough with the 'lyrics'. Here's some 'prose':
* 12 classes, both "stock" - such as mage, thief, cleric, warrior, and more original ones - vampires, nephandi, fathomers.
* 11 guilds - mostly places for newer players to join and learn the basics of the class of their choosing, but also wonderful places to meet people and learn a lot about the game in general.
* 7 orders for those more serious about advancing in the game, all with their original themes and long, rich histories.
* 4 deadly clans, each with their unique equipment and traditions.
* 3 mortal councils for those who wish to put their time into improving the game.
* about 70 areas, some of which are stock - though most of those were majorly rewritten, and most - completely original, connected by large "geo" zones - not just random settings of rooms like "wilderness" encountered in many other mobs, but areas huge in size and yet very well written and well designed; around 40,000 rooms, if not more.
* Tons of different equipment, for all levels and classes, from easily obtainable "ghetto" gear and up to major "pops" that may take weeks to acquire;
* Various equipment, as well as "glory" system to upgrade your items, create a complicated, fluctuating economy; trading eq is something more than just means to acquire items you want for those interested - it's a major part of the game, just as running or pkill.
* Numerous immortal-run quests, both organisation based, and open to all players.
* Well over a hundred players online at all times - and yet thanks to widely used channels and many organisations, all are more or less "linked" to each other in some way.
There's a lot more to it, though this review is getting too long already, so I'll just stop at here.
In conclusion - Realms of Despair is a very well-built MUD, and is definitely a must-see for anyone interested in hack and slash. Generally laid back and friendly, this MUD is also a good place to just chat and relax sometimes. Not so entertaining for hardcore rp'ers or playerkillers, it has some elements of both who enjoy either or both at times.