Via Mike Fahey's absurdly detailed World of Warcraft: Cataclysm liveblog, here are some of the biggest things to note about the new 2010 WoW expansion:
The Cataclysm in question is caused by the reappearance of the dragon Deathwing.
One of the two new races, the Worgen, is described as "the Wolverine of the Alliance" by Blizzard. Classes available will be everything but Paladins and Priests.
The other race, Goblins, are forced into service for the Horde and use a spiky racecar as their mount. Goblins also have rocket belts and can be, among other things, Rogues.
The level cap will be raised to 85, with Blizzard promising that the new five levels will be hard to get through.
The expansion offers seven new zones including The Lost Isles, Twilight Highlands and a sunken city that is, naturally, set entirely underwater.
All of the game's zones will be revamped with new items and new art. The map has changed, with the Barrens split in half and the Alliance losing control of Southshore. As with Wrath of the Lich King, there will be "phased terrain" that changes during the course of quests. There will also be two new starting zones and a zone for people level 78-85. Rising up through the classic levels has been revamped as well and is being promised to be an entirely new experience.
There will be 20 Guild levels, a guild talent tree and perks, such as slower durability loss, cheaper repairs, and mass resurrection. Also added will be a "Paths of the Titans" that will allow class-independent talent progressions. And there's a Mastery System, which offers players more power, the more points they spend in their talent tree.
The expansion offers new race class combos, including Tauren and Gnome priests as well as Dwarf shamans.
Players will now be able to fly anywhere and everywhere in Azeroth. And they'll be able to use underwater mounts.
There will be new Arena maps, rated Battlegrounds and a daily quest hub.
For even more details, check out Mike Fahey's World of Warcraft: Cataclysm Liveblog. Also check out these first screenshots of Cataclysm.