As Watcher suggests, these sessions can be beset by problems that can make the experience very frustrating. If you are interested in being one of the first to see the new encounters and are willing to spend the time giving feedback, putting up with the issues may be worth it.
It's open warfare between Alliance and Horde in Mists of Pandaria, World of Warcraft's next expansion. Jump into five new levels with new talents and class mechanics, try the new monk class, and create a pandaren character to ally with either Horde or Alliance. Look for expansion basics in our Mists FAQ, or dig into our spring press event coverage for more details!