It's sort of another moody monday for me. I've logged back into WoW and after what was a year of trying every other game, I'm actually happy. I'm at peace. I'm at this joyful and excited place that WoW is fun because... there are players. All of these MMOs I've played in the last forever long have been missing something: players. In WoW, no matter what quest, there is going to be another player to show up. The same in Destiny, to an extent, there is always someone nearby.
It's sad to say that new MMOs suffer from a situation in which they don't have many players in areas that players are needed. There is a huge lag in players reaching the endgame, so the ones that make it there first have to sit and wait forever for the endgame to develop. For those leveling, they are often alone in these huge worlds, because the mass of players who wanted to play the game day 1 have exited all of the zones and now these newbies are just running around. They hear a crowd in the distance and by the time they reach the crowd the game has... failed, at least that's how it is perceived.
Failed in the sense that it failed to bring in enough of a playerbase after the first 30 or 60 days that could tolerate logging in and waiting for people to reach max level. So the world is empty and the playerbase is scattered. ArenaNet was successful out of the gate with Guild Wars 2 for the fact that the world itself plays itself, not only that, but there is a major incentive to go back and do lower level content in the form that the rewards are justifiable and you get something for doing everything.
Yet other games, like WildStar, push the players into very weird segmented areas of the world. It's not fun and exciting to be in this giant field alone with no one to play with. Games like FFXIV on the other hand have such a small world that it's not hard to see other players doing anything since the maps are so condensed.
The key thing is tho that WoW has such a nice mix of other players that it's so satisfying and comforting to see all of the players around you and interacting with you, whereas in other games the other players are a rarity - even if the game is popular, the devs usually don't have enough time to test thousands of players moving through content.
Wildstar also made the mistake of multiple paths - which is GREAT for leveling alts, terrible for the game. It pushes players into different maps, which halves the already small amount of players that will be moving through content after the initial mass. Ticking off players day one with crowding issues is... oddly enough a good thing. Players respond well to the idea that they must fight to progress and need to camp enemies.
I mean, this is sort on topic, but YOU HAVE TO BE OKAY WITH BORING PLAYERS. It's just a thing you have to do. Spacing out content, making content easily accessible, moving players through content quickly, and offering alternative paths so players don't have to wait for quests is doing literally nothing but asking for your playerbase to be sad all the time because they're lonely and you're not forcing them to do anything exciting.
To put it in fitness terms - the treadmill is lame compared to the park. At the park you get both resistance from alternating heights and the extra fatigue and training from hitting pavement versus a suspension system. Getting on the treadmill and counting down 30 minutes seems like forever when you're just running through the park looking at the scenery and other people. It's harder, it's more difficult, but vastly more rewarding.
You can't put the content on rails and breadcrumb players through it and make it as easy as they can to do it. Unless you're SWTOR and you remove the excess side-quests to get players to do story missions which play out like a single player game in a game where leveling is the last thing anyone wants to do at this point.
Anyway, my point is, it's great to play with other players and it's great when a game forces you to. One of the reasons I think a lot of modern MMOs trip up is they think too poorly of their playerbase and assume the players want the easiest path with the least resistance, when the reality is the whole point of an MMO is to cooperatively complete goals together, with other Humans, and to do that sometimes you need to force people to hang out together a little bit.