Problem with MMORPGs is that there are too many variables and if you do a few of them wrong then, to me, it would defeat the purpose of making an MMORPG.
What I want to see in an MMORPG is PvE focused and catered towards the group experience. The content is not solo-quests; the content is you delving in dungeons of various sizes and difficulties scattered around the world for you and your friends to discover. Instead of giving you errands to follow, MMORPGs should set us free choosing our own pace. Quests should be more intimate, something that takes a long time for you to complete and the reward is great. But the whole point of playing is "the chase"; just like TCGs where you chase that mythical/rare card in an MMORPG your main focus is to chase that rare gear. Problem with most recent MMORPGs is that gear is thrown at you left and right so easily and so fast and you level too fast and upgrade your gear too fast it really doesn't matter at all. Gear is meaningless until you reach max level, this design philosophy should die.
So, "the chase" is you seeking that rare boot dropped by the vampire lord. It's as simple as that. The content should be challenging and fun with "roles" for each class. Don't listen to those who say "trinity is horrible"; actually trinity is horrible there should be more than just three roles. Roles are important in an MMORPG you need cooperation between players, you need to make players feel they have a role to fill in a group. Also, the community interdependence is important; several non-combat skills that make the life of other players easier (like Druid/Wizard portals in EQ). Another chase thing is gaining a skill, level, spell...etc. Make it hard enough to be worth while. If it's too fast, too easy and too trivial then there's no point in seeking it.
Again, a world filled with dungeons and their lore. Dungeons of various levels, sizes and difficulties. The dungeon is your main bread and butter; not quests. Scratch this "errand" style of quests and give us meaningful optional quests that take time and effort to achieve with amazing rewards.
I am unable to play an MMORPG were I have to solo-quest for hours. This, I cannot do. I will not cope with that "quest" style of MMORPGs, I'd rather shove a fork in my eye. I need freedom to test my capability with NPCs; I can go deeper in the forest to fight harder monsters or stay where I am fighting easier monsters. I decide my own pace. Monsters should not die in a few seconds and they should be difficult enough to warrant casual group play. If the average monster is too easy and dies too fast; why would I want to group with my friend? I am bored of playing solo in an MMORPG. I want to see monsters that take a long time to take down. Monsters that makes you definitely consider grouping.
This is only part of what I want in an MMORPG but I believe if designers do this one right I would be interested.