A Graphical Upgrade
World of Warcraft is over four years old at this point, and while its art design has let it aged gracefully, it has aged nevertheless. Wrath of the Lich King introduces some incremental improvements, such as a nice shadow system, but it'd be nice if Blizzard could give us a bigger graphical bump next time. The game could certainly use higher-res textures as well as better effects.
Better Support for Mods
Along the lines of an interface overhaul is better support for third-party mods. There are tons of them out there that improve the game in many ways, but to discover and install them requires you to work at it. The web browser Firefox has a great add-on tool that helps you install and maintain third-party plug-ins and skins. It makes it easy to find new add-ins and experiment with them; if you don't like them, it also makes it incredibly easy to remove them.
More Classes
Wrath of the Lich King introduces the first hero class to World of Warcraft, which is great, but we'd like to see more classes introduced more quickly. Waiting two years for a new character class is a bit long, and at this rate it'll take a decade to build up a decent stock of new classes. Couldn't this process be sped along?
Pirates!
Ever since the early rumors about the South Seas expansion prior to the announcement of The Burning Crusade, we've wanted the ability to take to the seas and engage in keelhauling and talking like a pirate. This could provide a great way to deliver some booty, as well as explore whole new continents or islands.
Public Quests
Yes, this is taken from Warhammer Online, but we love public quests. And if Blizzard does anything well, it's to execute better on other people's ideas. Remember, the good ones borrow, but the great ones steal. Public quests are great because they let you engage in some epic battles with impromptu groups of strangers without having to travel to another instance. You're just traveling along the path when you come across a huge battle. Jump in, have fun, and get great rewards. Do it, Blizzard.
Pandaren Brewmasters
Okay, what's cooler than anthropomorphisized pandas? Nothing , and that is why we really want Pandarens as a new playable race. Look at them, aren't they incredibly cuddly and cute? And the brewmasters are the coolest of the Pandarens; these wandering warriors would let you relive all those memories of Kung Fu, the television series.