I've been and am thinking about this alot. I grew up around UO, back in the day just schooling myself in the first and second grade.

The tinkering part of my mind quickly grew tired of the free shards I had around in my country so I started investing more time into learning about UO, shards, scripting and all the other stuff. (I haven't played the official shards, ever)

To be honest, I cannot recall older memories of me involved in scripting than the ones provided through UO and Sphere, and guess what - I've grown to be a software developer.

Then, to my software development side of brain I got the playful, youthful creative part, which also is driven by the juices from UO. Holy smokes, the material system blew my mind. The freedom, the possibilities... then combined with scripting where you could develop it even further - snappers. This has grown me into a hobbyist game developer, though, I am transitioning into it fulltime.

So yeah, UO really fills a special place in my heart.

Now, I didn't have many hardcore friends around that really dug the UO worlds. With WC3 and DotA rising - some switched there. CS was/is, probably, the most played game in our country, so, the community itself took a great chunk of members.

And, eventually, at my early teens, with my mom in a computer store, I saw the beautiful box of WoW, the vanilla one. I got hooked by the dwarf and elf on the front and I went on to convince my mother of buying it for me. Well, after the consultant had put the "it's a subscription game, aye - you need to pour money every month to play it" question on the table.

I think I managed to get to level 13 in WoW, when I switched it off - "fuck, I don't understand a thing, this is hard". Though, I had made some virtual friends already. Half a year to year later I switched back - managed to get to 34 - still not convinced. At the offtime, I was working on my freeshard and playing some CS (I skipped school a lot for these 2 games). After TBC came out and just before the release of WotLK, I gave WoW another try and I got hooked, heavily.

Now, I haven't really played anything else in terms of MMO... I have tried some Korean spinoffs, but they eventually led to me playing WoW again, and gnaw my teeth deeper into the big chunk of flesh it exposed.

Though, a week after defeating LK, it took one minute for me, to realize, that WoW is as empty as a potion bottle in UO, maybe even more emptier. I realized it through my creativity and software development experience, reverse engineering not only the mechanics, but also the marketing, social aspect and the esports layers of WoW.

Haven't been hooked to anything ever since... Now, this build up is just to cover the back of my upcoming theory.

Accessibility
WoW didn't rise to it's fame just because it provided the dumbed down model of "kill 10 rats". It actually at some times is even worse, because after you have killed those 10 rats, it gave you the next part of the quest, which led you back inside the same ratcave to kill the rat miniboss. Why couldn't you tell this instantly, right?

But the thing is... That's how WoW introduces itself. The vast world, the possibilities, the dangers, the distances, the grind, the patience. And all that combined is actually flawless and edutainional (education part for the game itself) game design that not only CAN, but COULD and still DOES capture not only the gamer minds (we, the hardcore family!), but consumers of entertainment - everyday people, business people, grandparents.

The problem with that, is that it becomes stale after some playthroughs. Not only stale, but utterly boring bordering with depressing (which is why I left). We simply grow out of it. The game is made such that it can be outgrown. Not by design, but that's the psychological side effect of it that probably no one understood, thought of when they built these worlds. The ones remaining are the ones that captured communities inside the game around themselves, not got captured by others (Swifty and other peeps).

In other words, WoW is simply an interactive tutorial all the way through. And the first time you play it, you actually enjoy it as it is very demanding yet possible and hence rewarding (Flow). Think of just what you have learned yourself by interactive guidance? Same applies to the general entertainment consumers - they could enter the world with no problems.

Did UO have this? The social aspect provided it - friends teaching friends and sometimes (in e-cafes) enemies teaching enemies, just to get the most out of it later. Though, the social aspect works only when you have community. Has UO ever provided a clear-cut entry level path for everyone?
Maybe now, with their latest expansions, though, that's not integrated into the core anymore, hell, the core is at SotA - though, watching their development over the year, I cannot seem to find the essence that could farm the everyday guys.
I doubt that even Shards online will provide anything good, given that the ones that claim that have been working on UO, are the ones that came after OSI.

Mechanics
WoW has got to have the worst combat I have ever encountered in video games. Probably because the most rewarding combat experience I have had, is, from the competitive shooters such as CS and Quake.
No, it's good, well... "enough for the game", but in relation to the size of everything around it - the combat is shit.
But combine that with accessibility, the huge and various content around it - would you really be that interested in crazy ass technical, demanding combat to clear all the content? For a week - yes, for a month - yes, for years - fuck no. The context together requires the combat to be as dumb as possible, such that the heavy grind wouldn't consume too much energy.

And then the factions times races times classes times talents times styles. Look at it through psychology. People could find what fit them the most, what fit their imagination the most, what fit their fears the most. And plus to that - people do not know what they want, which the sandbox world of UO emphasized on doing - do what you want, how you want it. But if all the "I want X" questions are such a struggle to answer, it ends up a little bit too anxious, maybe not consciously, but in the levels of subconsciousness - definitely.
At the end of the day, how many distinct characters have you rolled in UO, that are meant for day to day interaction within the world?
And, isn't the end result actually comparable to the class/talent/style system UO provides?

I for once, how I started mining/blacksmithing, have stayed with it. Currently, yes, I am investing my time in other skills, simply because I'm researching the game design behind UO - the pros, the cons.

Accessibility * Mechanics * Meaningful content Accessibility is the greatest factor why the modern MMO's actually lift off. The entry level being the most crucial one, followed by transition to competency and full awareness. Endgame is simply the culmination, which is also scaled fairly good to keep you entertained. Most of the games fail at the entry. Not only MMO's.

Another great factor for MMO's is the content. Yes, you can have choppable trees, destructible rocks, killable rats, dungeons with rooms and zombies and skeletons within them - but how meaningful the content is? What challenges does it provide? What knowledge you require about progressing through it and how much more for it's completion?

And then the best part is how all of this extends into mechanics and the balance around it. Welcome the Tank, DPS and Support - the generic styles of any modern MMO. I actually just thought about how these are the "three stars" of "level completed" in any modern mobile game. The glory of it all.

Just think of how the mechanics of these distinct roles play into the hands of meaningful content that becomes even more accessible when you combine them.

Quests completable by clearing dungeons, that require comrades that play a distinct role and know their role and importance within the world due to quests that propelled them into understanding their role even more. Dungeons give better rewards, so, it's an obvious choice.

Economy This is where modern MMO's shine the most...

If accessibility builds, mechanics solidify and content tames the community, economy is where it all clashes giving that replayability and cementing the social aspect.

WoW also has accessible and straight forward crafting system, where every single one of the professions is crucial in any stage of your characters career. Was it gear while levelling (this is dead for quite some time already in WoW, the gear crafting professions are useless), be it enchants, be it support items, be it glyphs - you NEED others.

The aspect around quests and instances are a form of economy itself, that have their own inflation and deflation. How many Tanks are there, how many DPS, how many Supports? How good are you? How reputable are you?

to be continued in reply...