PvP - either there’s too little or its not implemented right (only DAoC had this even sorta right). There needs to be a natural and pretty horrific consequence for someone that’s level 1 quadrabillion one-shotting a level 7 and spitting on their not-yet-cold corpse.
Combat - either its too slow or its not engrossing enough (you hit the same button sequence on your bar over and over to kill virtually every stupid mob).
Customization - not enough options to distinguish yourself from the other 10,000 nerds playing. If I want to play a fat merchant, let me slide the slider bar to decide how morbidly obsese I want to be in char creation.
Economy - screwed all to hell because of IGE and eBayers selling gold/plat/gil to 12 year old ninnies. Should be locked down so items are bought with energy or something that drops from mobs which is bind on pickup and can’t, therefore, be bought or sold or traded between accounts.
Mobs - lack of variety, lack of AI, lack of sense of accomplishment when they go down, they’re there 2 minutes later and appear out of thin air? How realistic!
Wimpiness - your player starts off basically naked and then gets some dorky clothes and corny weapons for putting in the first 10 levels. What a reward!
Classes - players have to choose classes as they level. It ought to be skill-based. The more you do a certain thing, the better at it you become. You can be a jack of all trades or super skilled in one area. Like in Ultima Online or Dungeon Siege.
User Interface - Not customizable enough. I want skins for my GUI. I want transparency options, resizable, movable, font-changeable options. And for God's sake, don't make me look away from my character during combat to see if I have enough mana or health left!
People - There are some real jerks that play MMO's. We need a really good system for kicking people from group, putting them and all their toons on ignore and adding them to a guild blacklist.
Originality - I don’t want the used up, cliched dwarf, elf, human, warrior, rogue, caster races and classes. Make something new. Something exciting.
Balance - Everyone should be able to solo effectively. Not just if you have pimped out gear and get a guildy to buff you because you specced a certain way that gimped you so hard you can barely solo a wimpstyle mob that’s your level.
Partying - There should be no penalty for grouping together and no bonus for it either. The experience you get should come from skilling up, not farming items or gold.
Dying - You get a multiplier for staying alive longer. If you die it zeroes out and begins again.
Stuck - Options for people shy of having to contact support and waiting 20 minutes for a company payed GM to help them with a simple /unstuck command the player should have been able to do themself.
Quests - Player wiki-able thotbot ingame, allowing players to help write the user guide and make corrections, taking pressure off the dev team come patch night to fix all the little bugs.