You know what would be cool? If magic worked like magic in the game, instead of just a means for damage. Let dungeons be dark, so a melee guy has to use a torch, or a wizard could summon a fire wisp. Maybe let Warlocks have summoning circles, requiring 5 Warlocks, each with a rare component, to summon some ungodly demon thing. Maybe use other things other than mana as currency for spells, like maybe health, or experience? What if I could sacrifice levels of my character to a Necromancer for something cool in return?
Rare reagents, rare and dangerous spells, etc.
And for fuck's sake, have closed doors, locked chests, and actual traps so Rogues having something to do other than stealth and back stab. Christ.
Basically I think MMOs need to go to a more... Hands off approach. The genre needs to immerse itself more in it's roots (D&D) rather than stream lining the shit out of everything.