I can tell you EXACTLY what I want in an MMO. No idea if I will ever get it again though seeing as the vast majority are matrix'ed into the WoW MMO "concept".
Here is what I want.....something that contains (at the very least) the following -
** A skill based system where use increases the skill
** A enemy system (be it player or monster) where I cannot tell what level it is or how safe I am to attack it. Let me learn that myself by trying.
** A deep crafting system, woodworking, metalworking, jewelcrafting, tinkering, upholstery etc etc
** No overhead names on players, so that in pvp players can use the terrain to set up ambushes without names sticking out
** A deep housing structure which is located within the gameworld itself (rather than in seperate instances), either via plots or free placement.
** Built in voice comms
** A non-coloured looting system, none of this green items, blue items, yellow items, tartan items.
** Non-instanced dungeons, actually, no instancing at all. Absolute minimal zoning too (preferably none).
** A wide variety of skills and abilities, including both the useful and the non-useful fluff skills
** Dyes, clothing, weapons, furniture, carpets, everything that would be dyeable should be dyeable
** A decent amount of dungeons, varying in sizes from ones that take 30mins, to ones which take several hours. Preferably dungeons with dynamic puzzles within, rather than just run and gun dungeons
** Talking of dynamics, a dynamic weather system which affects the characters, ie, you move slower in snowy conditions, rain increases lightning damage etc.
** An active and vibrant economy including an auction house
** Mounts of varying types and speeds, purchaseable from a reasonable level, and mounted combat.
** Dynamic terrain, even if limited, for instance if I cut down a tree for wood, then the tree should actually get cut down and regrow (accelerated)
** Player run shops/taverns/vendors etc
** Ships/ship combat/sea travel/underwater areas to fight and explore in
** Death penalties, whether it be your items being lootable or some other penalty, but make it so that there is an element of "fear" about dying rather than people purposefully getting themselves killed as a way to travel quickly
** Books/Scrolls/Noticeboards that can be written in/on by players, some way that players can build up a literary history/lore to the game
** Widespread pvp, with towns/castles/forts/major resources/locales which can be captured
Um...yup...I am sure theres more, but thats a start towards my ultimate MMO.
I should add that a lot of the stuff listed above was done in UO, over 10 years ago. The fact that modern mmos are so restricted in what you can do is imo, indicative of how the MMO genre has generally gone backwards since 10 years ago, rather than forwards into what virtual worlds can be.