I've been playing MMOs for years. I played Ultima Online, Beta-Tested EverQuest, and I'm back to playing Old School RuneScape now, just to name a few.
You play MMOs to have a huge open, ever changing world. Some of us, myself included, prefer to 99% of the time, tackle that world and its various tasks solo. I want to see other players playing, interact with them, trade, and yes, even group on occasion, but I feel the best MMOs out there make sure that the entire content of the game can be enjoyed whether you enjoy playing as a group or a solo player. This is one reason I was not a huge fan of WoW. Besides being quest driven, it also had several specific quests/raids that necessitated a minimum number of players go in to take on the baddy. This could be ignored, if taking on said Baddy wasn't part of an almost mandatory quest chain to get past a certain point in your character development, but in WoW, that wasn't the case.
Now, EverQuest did it pretty good when they brought in the Dungeon Instances, were you could do a short term looking for group raid of a specific dungeon, but the dungeons themselves were extras, and not required in order to progress your character along.
A great MMO needs to remember there are both Solo'ists and Raiders out there, and cater to them both. If someone just wants to sit and craft all day long, they should be able to do just that. If they want to take on the monsters of the world, on their own schedule, without having to group to do it, that is also viable.