Quite frankly, if I can get a decent countdown timer bars for buffs and debuffs, a hud (like WoW's IceHud), clean unit frames and configurable button bars ... I'll be a very, very happy player!
One of Blizzard's keys to success was realising that a allowing players to fully configure their interface gives them a sense of ownership and creation; they can't create in the world, they can at least create how the look at the world ("This is my UI. Isn't it cool! See all the things it shows me!") If Turbine can mimic that, they are on a winner.