how is the gameplay dated??
I don't mean for this to come across as forceful as it inevitably will, being a list of criticism and all
So, I'd like to preface that I'm not trying to steamroll anyone, and I'm only quoting you Salivern because you pose it as a question which makes it a suitable start point.
Also, that I'm not trying to say that Ultima Online is bad, or that people can't or shouldn't be having fun in it. I do
I know the obvious response to comparisons with other games would be that I should play those games, but I include them as examples of modern design as a contrast.
Skill training is almost entirely based on repetitive action.
For all their flaws, modern MMOGs temper their XP chases with a journey. Your skills/levels increase as you travel through a series of areas with escalating difficulty.
Ultima Online has no defined journey, being a sandbox.
To try to find some mainstream examples, consider the Lord of the Rings films. The modern MMOG is a journey, you start off at the New Player area, and set off on a journey, and along the way you "grow" as a person, gaining perspective and skills.
Ultima Online is more like the Karate Kid. The "journey" is one of waxing the fence, sanding the car and painting the deck (however without giving the player the benefits of muscle memory or better reaction times).
The world is lifeless.
Now comes the first comparison; Skyrim.
If you play Skyrim, one thing you'll likely notice when traveling to some destination is the world around you.
If you run up to a deer, it'll bolt. If you run up to a bear, it'll roar at you, then attack if you ignore the warning.
If you get into a fight with a pack of wolves, they'll try to break off and circle around to flank you.
The world responds to your presences, and as such feels alive.
In Ultima Online, almost everything from nobles to rabbits shuffles around like zombies, completely indifferent to their surroundings.
The quest system is lacking.
I say system, but of course there's three.
There's the original one for the Doom Gauntlet and Solen quests. There's the newer one used for the Heartwood quests and a lot of others. Then there's the quests that aren't explicitly quests (Halloween a few years back, for example).
Whichever one you look at, there's just been a lot of advances in that area over the past decade, which aren't present.
Grouping mechanics.
I'm going to come across as my most scathing here, but there's really not much good to say about the grouping mechanics in Ultima Online.
They exist, so I guess there's that. But the party system as it exists with basic functionality is limping. What functionality there is barely works, and half of what there was doesn't work properly (or at all).
Grouping mechanics are the keystone of cooperative gaming, making it easier and perhaps more rewarding to group up with others means people group up more.
Warhammer: Age of Reckoning had "open warbands" which were like public parties, most modern MMOGs have loot rolling mechanics (need/greed/pass etc), Star Wars The Old Republic gave "social" points for participating in conversations as a group, Star Trek Online would group you with others on the same quest as you at the time, Planetside 2 has voice chat and XP bonuses for being in a squad.
I'll leave it at this, because being overly critical makes me sad