Not my cup of tea since they tend to be so repetitive.
That said, I have known a lot of people who love them. Black Desert, PSO2 (which a lot of people hacked to add English before the game was localized here), and FF XIV are the most common ones I hear about, but some of my friends play other ones. I thought GW2 was a massive improvement over pretty much everything wrong with WoW, but that game is pretty old (though still well-played). Notice that none of those games are American, the genre is a lot more popular in Asia.
A big part of that is cultural, since Eastern people tend to value mastery of one [game] over competency at a dozen [games] skills. That mindset makes the massive amounts of content in MMORPG’s more appealing, and makes them more willing to pay extra for certain in-game content (since many only play one game).