Blizzard is laying the groundwork for its next World of Warcraft expansion, Mists of Pandaria. Before you jump into a world of pandas, the game client will receive the 5.0.4 patch. The biggest changes come to classes and the new talent system, and there's plenty to check out.
The WoW Blog outlines the changes, going into great detail about many of the class changes. The new talent system lets you open up a new talent pane, showing Core Abilities for each class, along with a variety of new and old abilities. You'll have to make hard choices about which ones to equip, but you can always respec with a Tome of Clear Mind or a visit to your class trainer.
Other changes are coming to the Glyphs system, cooking, account-wide pets and mounts, a help system, and tweaks to its MMO roots. The full list of changes is pretty massive, and it's not even the full patch notes. We should expect some pretty major changes coming when the patch hits tomorrow.
Mists of Pandaria comes out on September 25.