Buuut .. "many MMOS" which have Wurm-like features do not have all the features offered here, rather one or two of them, and very poor implemented.
(Let me give you only one example: riding.
From the old Oblivion (and the entire Elder Scrolls franchise) to the newly Animallica (in early access) games, you can ride and "have" horses.
It is a painful, hurtful, traumatic experience, your horse is horrible hard to command, you cannot do anything while mounted, you cannot breed your horses, you cannot gear them (unless you call "gearing" paying a stable owner to throw something on your horse, which you have no control on) and generally you cannot interact at all with your horse, a not so nice designed pixelated animal with weird anatomy or dead fish looking eyes.
On the other hand, in Wurm riding is a pleasurable experience, you can do 101 things (and some others I forgot about) while mounted, you can breed your horses until your deed ratio falls bellow the sea level, you have a lot of things to put on them, for look, speed, protection, different looking and, oh yes!, some dyeable gear now, you can groom, tame, fsb a horse, give a nickname to your nanimal, your horse goes through different life stages, it can be cared for, hitched, transported over seas, as for the design, what is more to say than look at those many colours!! look at the thread with screenies of new born baby horses!!
Please note that riding a horse is ONE thing you can do in Wurm, and it comes boxed with so many things tied to it, you rapidily lose count of them! Add to that that each and every of those things is also boxed with so many things, which are boxed with so many things, which ...)
I'll rest my case here.
I am sure most of us played a lot of other MMOS.
Listing what unique things you can do in Wurm means you can do all of them in the same game, not in 20-30 different games put all together, and even so you wouldn't cover all the options you have in Wurm.
Wurm is so complex, it doesn't have any "competitor". Nor will it have one in the near or not so near future, considering the trend in gaming industry, which seems to be pulling us back to the late '90s - early 00s, with simplistic, lifeless graphics, basic features, linear and short stories, "go there, kill 5 bandits, bring back their house goblins as proof" quests and 3-6 months of playing time (6 months, riiiight! .. but I felt so generous).
Wurm is so complex that it turns out to be another life on its own. Boring, less appealing, annoying, frustrating, yet so much of your own in its full splendour, glory, hopefulness and joy.
Enjoy it while it lasts and get the best out of it while you can.
What unique things can you do in Wurm?.. How about tell Nessie a joke and make it laugh out loud?