WoW FEELS super fragmented right now.
I mean, when they finally gave in and released Classic I had no idea they would release 10 different versions of it. But that's mostly a different topic.
The shattered world of the main game is the big problem, cities and raids and events that exist only conditionally, like Undercity and Ny'Alotha with the attatched invasion.
Being able to meet and talk with players you can't trade with or craft for, whether they're Horde while you're Alliance, or they're from an unconnected server to yours. When you tell the latter they can send you a personal crafting order for the sword they keep asking for in Trade Chat, they can't.
And as a Blacksmith/Miner main, I get to experience the shattered state of instanced zoning more regularly, every time I fly out to get ore, with several ore deposits simply disappearing as I approach them or start mining them. I see them from the other side of a fracture in the world. When I cross over, the illusion fades away.
That's partly because it's now more important to know what you're doing, than figuring out what you're doing, or just enjoying the fight. Unless you're willing to just tank insults while playing, and rebuild and retry with constant leavers, you have to study. Usually people try, but often they sit back and give in to "experiencing" games through video instead.
WoW for example has almost no tolerance for flawed teammates anywhere anymore, I've seen countless groups that would rather sit outside a dungeon for hours, than be inside it for 15 minutes too long.
And people no longer think "if you want good teammates, you have to build a team", they instead think that everyone who joins the random matchmaker has a responsibility to be good. It's rude to be bad at World of Warcraft.