I've been playing MUDs for around 13 years now. Most of those playing a MUD called Icesus. Not the most popular but not deserted either - around 50-100 players online at any given time.
I've yet to see a MUD with better combat system (though I haven't been looking for years). I really wish some good MMORPG would implement a decent combat system with enough modifiers such as player stats and skills, weapon material/quality/speed/stats/other modifiers, enemy armor type/quality, hit slots, resists and a dozen melee skills affecting your every hit with some luck on the side too (what a messy sentence, basically a lot of modifiers for every single hit you deal to add depth to the combat). Add in couple of hundred different skills doing various things in combat and outside of it, half a dozen different melee guilds, another half a dozen spellcaster guilds with vastly different spells and mechanics. And masteries. And trainable+learnable skills. Areas that contain very little combat but other tricky mechanics, epic bosses that take up to 12 hours to kill, unique items that in addition to stats have wildly different special effects, crafting system that takes enough time to master, blessings, random events, leveling system that makes it practically impossible to reach the maximum level and the list goes on.
But no, MMORPGs remain very simple and they dare to ask us money every month too (most MUDs are free). In MMORPGs you have your x2 crit modifier, few buffs and that's about it for combat. You might even have to move out of the fire or *gasp*, follow a few timers. World events rarely do anything and the game often feels very static and grindy. Items are rarely randomly generated and in very few MMORPGs do much more than just have stats and damage. Some weapons in for example WoW have pretty basic procs/special hits but nothing with depth.
I doubt anyone can read the above without losing their mind trying to understand it but my point is that MMORPGs have a long way to go to reach the level of MUDs. Sure, MMORPGs have fancy graphics but that's really all they have. Those graphics take too much development time to allow deeper gameplay elements. I'm waiting for the day an MMORPG can rival a good MUD; that will be the day I can finally leave my text based games and really move on.
Ps.
Mudconnect currently lists 1115 MUDs that are more or less active.
I'm thinking of pestering a bunch of people I used to play this with and starting from scratch with new characters. Old skool! Sure this will give my 4890 a proper workout! 
