Hay, good topic.
I will list my top five in no particular order, though of course with the caveat that I am still trying muds out and have more to investigate, both for the db and for personal preference.
1: Alteraeon. The more games I try the more I respect alteraeon.
Combat that is interesting and gives you lots of abilities to play with rather than just typing "kill" and wailing away, lots of items preparations, very well written zones and quests that even reward you for exploring.
This is of course quite aside from the soundpack which virtually makes it a full audio rpg.
2: Cosmic rage: many great activities, a friendly player base and frequent updates, also great to see a space world not dominated by pvp. The soundpack is good too.
3: Frandom: probably the most unique mud for advancement being that killing means nothing in this game, huge amounts to discover and a beautifully described world with a very rich and coherent history and law, not to mention very friendly admins and other players.
4: Clok: still the best for craftingand exploring and a realistic experience, I particularly love theand survival in this one, with the many activities that you can learn and master.
5: The sadly departed Wayfar1444: I feel a little bad listing a mud that is no longer around, but it's a dam shame since I spent many happy hours here setting up my space colony, exploring the randomly generated planets and building literally everything! from camp fires to trucks (I never quite got to build my own starship but I was almost there).
Also an actually sensible remort system that it was possible to progress through rather easily and get rewards from.
I dam well hope the game comes back up.
Others I have tried (ie, played for long enough to get into and have a basic idea what they are about), and some brief thoughts:
Aardwolf: A quick and easy pick up and play game, great for sudden bursts of fighting and instant autoquests where advancement is fairly rapid (albeit there is a long way to advance). Particularly nice for shortcutting a lot of things like needing to minimax equipment or hunt around for mobs, freeing you up to sit back and enjoy the descriptions and the carnage.
Area goals however are rather unfair in this one and autoquests can paul after a while.
Erion: Like aardwolf but with more coherent zones, far fewer players, actually more interesting and unique combat, as well as a host of little extras from events to random item drops to player run house organizations with different styles and competitions keep things interesting.
The only really major problem with erion is that advancement is rather slow, unless you constantly play in hardcore mode.
more missions are being added to the game though,, so this is probably one to watch.
Classic six dragons: Quests are really good here and area sdescriptions and theme is great. Combat is also more interesting since you tend to get fewer techniques and spells that matter, but make more difference, there is even crafting.
The only problem with six dragons is again, advancement is a little slow.
Oh and it has a good soundpack too.
7th plane: A great mud for systems and exploring, especially you pretty much njeed to find everything yourself. I just really! wish there were more descriptions.
4dimentions: wonderful crafting, beautifully written zones, and a veryand unique fun theme.
Only problem is quests are reeeeeeeeally obscure, and other players aren't particularly good about sharing information about them. Combat isn't as fun in this one, since your techniques and spells don't do as much, (though ranged combat is rather fun), however this is a game more about the questing and exploring, in particular the crafting is wonderful and a great way to advance without getting board with monster murder.
Fluxworld: Again, this is rather like frandom and a game with virtually no combat. The theme and setting is wonderfully unique, being set on an alien planet in the future, you can simply wander about and explore and poke your nose into things.
However actually finding thingsdo, either quests, crafting activities or whatever seemed a little difficult, meaning this one is more like being tourist than playing a game (though some of the in built puzzles are fun, ever fancied playing human mine sweeper?).
MAteriamagica: Wonderful random wilderness map and exploring, and some unique races and classes. Combat seemed a bit long winded, but on the plus side things like elemental effects, different weapon types and attacks etc looked fun to play with.
The only really major problem I had in this one was that finding stuff to do was very! difficult being that when I played at the time, generated quests from an official quest giver were time locked and marks, aka, quests you discover from npcs were capped, meaning you could literally level yourself out of doing stuff.
This meant either you had to spend a lot of time playing with an open wiki, or wander around at random hoping to stumble upon things, neither of which really appealed, though in fairness I believe some of these tendencies have changed more recently.
Star conquest: Amazingly written setting, beautiful descriptions and great theme. One problem? Super spammy, impossible to do withyout mjajor rescripting combat (and a dev team who forbid rescripting). Not to mention the fact that basically if you end up losing your spaceship your told to literally go and beg other players since there is nothing else you can do, ---- sorry but I really! didn't like this game, so much promise, and such a disappointing experience.
Cyber assault: interesting theme, good story and some unique sounding activities, being a cyber future themed mud. The problem I found was very spammy combat and little by way of changes for screen reader users.
it is worth noting though that I was rather more a novice at muds back then and either I might have missed something about setting or other options, or the game might have changed.
Avalon the legend lives: I know I've been throwing around the term "beautiful descriptions" here a lot, but Avalon is simply a work of art, I particularly like the way you notice more of the world and more things described depending upon your character.
The problem I found is absolutely everything! after newbie school is dependent upon other players.
This means you can't just go off and explore since you don't even know how to stop yourself starving, but need to wait for someone be online enough to explain and help you out.
The mud has help files, very very extensive help, but the help is so! complete it's dam difficult to know where to start, indeed the help spends so much time telling you how much there is generally to do in the game, is actually hard to get specific info.
I really! want to like Avalona game with this amount of detail and this clear amount of work is planely a work of love, but I've tried three times to get into more of the game beyond the newbie academy, and each time utterly failed.
it's not even that other players are unfriendly, it's just that when you ask for help they tend to point to the help files, which as I said aren't specific, --- eg, they will tell you to do the equipment badgeand offer to help[ you with that, and even give you ltos of items they've made, but not how to begin earning money in the game or really where you can go and what to do.
I'm genuinely sorry about this since Avalon is like gorgeous feast behind a glass wall, I'm sure it would be awesome if I could get through that glass!
Diskworld: Again a very similar problem to Avalon, though other players there were far less friendly.
I do the newbie tutorial then spend my time wandering anchemorpork with nothing else to do but fight street ravens.
Help indicates lots of activities and quests, and even a system of learning by doing rather than by distributing xp, but no idea how to start any of them.
I was particularly disappointed that so many colourful characters from terry Pratchett's books such as corporal knobs or Moist Von Lipwig were just window dressing and weren't possible to interact with.
I'd say that is all muds I've played seriously enough to actually comment on.
Others like the now vanished project bob, promethius, lament, luminary, 3 kingdoms, cleft of dimentions or lensmoor I just never really got far enough to say anything concrete about. Epitaff I found the combat too spammy to even get through the tutorial (though I think that got fixed), and indeed Empire mud I was putoff after the first hour when trying to setup my empire by probably the least friendly player base and creator ever! though to be fair the game is in a new version now and it's possible the issue I had with finding land in a very crowded world to start building no longer is a problem.
Hay, this turned into more of a rant than I expected .
With our dreaming and singing, Ceaseless and sorrowless we! The glory about us clinging Of the glorious futures we see,
Our souls with high music ringing; O men! It must ever be
That we dwell in our dreaming and singing, A little apart from ye. (Arthur O'Shaughnessy 1873.)