My "Perfect" MMO (without using other MMO names):
A realistic world/characters filled with breathtaking animations ranging from spells/attacks to Cut-scenes etc.
Big towns that are fast to navigate (maybe even have an in-town railway system to jump on real quick).
It would have jump but it would be class specific animations. (example: Lancer would thrust up with his polearm, mage would use a spell underneath his feet to gain momentum etc..., there would be a delay due to the animation and landing so you could not spam it like bunny-hopping)
There would be a vast array of quest-types to do. However progression would not just be: click this quest and go here, continue to max level etc... Depending on Quest-type reward would be based on the # of players, difficulty of monsters & the time remaining (reward would be EXP, Money, Armor and/or Random Reward Box).
Regular monsters all across the world would drop very basic gear so you always have something to upgrade to even if it sux. You would be able to add stats with a sort of slot system if you choose. The stones to place in slots would drop from all monsters (not too great stats, unless rare NM) and the better ones would be crafted or dropped from very special areas.
EVERY single zone would have a "% completed" collection for fun. In the main interface you would view the objectives that you needed to do to complete a zone 100%. Achievements for 100% would likely be along the lines of a nice "gemstone" or a special glow/icon around your character while in the area. Treasure rates also would go up a little while in the zone. Little enhancements like that.
Not just a "card game", but several (10~) mini-games all across the world. Different "cultures" would have different games that you could play. Part of doing this would be for collection and competition.
PvP. I'm not the biggest PvP fan, but you could duel anyone if they accepted or "rent out" an instance of a zone to have larger battles in (like towns or battlefields or something). There may even be a sort of friendly "PvPvE" that you and your friends place monsters in an editor and then you all enter to see who can kill the most monsters & reach the end while killing each-other to slow others down.
Built in to the interface would be the ability to access tutorial information, guides/recommendations & official forum along with bug-reporting.
ALL content would have a sort of bill-board at the entrance for players to vote on the enjoyability/fun/challenge. They would only be able to vote after doing the content at least 1 time and would need to wait about 1 month or until developmental changes to that system to vote again.
There would always, at the very least, be bosses included in most content at the "end". However, there would also be very memorable bosses for much more challenging content.
Guilds would level up from the progress of everyone in the guild. The rewards would be like passive traits that are applied to everyone in the guild. There may even be a sort-of "talent tree" for a guild to choose.
Leveling up would only get you so far, but defeating bosses would be necessary for "unlocking" things to progress your character even further (ex: killing MegaBoss #1 = Higher impact of VIT on DEF & HP etc, Boss #2 = Ability to use another slot on armor for your "gemstones" etc etc).
Bah, i can't add any more, busy and gtg. But you can sort-of imagine how it could be. Bottom line is no straight-line to max level and always fun content for all levels (mini-games).