I also gotta agree with Oscar on his analysis of mmo's here.
If we are arguing mechanics I think it kinda falls along here:
Wizardry and its clones (this includes SMT), roguelikes, Infinity Engine games, Diablo 1-3, dungeon crawlers (not to be confused with roguelikes and wizardry-likes, though there is some overlap) -> mmos -> most mainstream rpgs ranging from Square stuff, Nintendo rpgs (though the main story in Poke'mon only), Bioware rpgs, Bethesda rpgs, Obsidian rpgs, about anything mainstream and successful.
I haven't played Ultima games aside from 4 so I can't argue its mechanics.
mmo's main appeal comes out when you're in a group. As a soloist, I find them fairly boring, and just tedious affair, though WoW had good moments as a Rogue where I had to sneak around Alliance places without getting caught, and that was great.
But when we get into story, plot, worlds, those single player rpgs blow mmo's out of the water.. Though games like Diablo and Titan Quest suffer tremendously here.
I think the one thing that mmo's do better than most single player games is the sense of scale and adventure. Traveling in an mmo's world, and finding new places, and the allure of being ABLE to survive making it to a new place is, aside from the social aspect, the only major thing that ever appealed to me in mmo's. I love the sense of scale of mmo's, they do that wonderfully.