Square-Enix recently had a conference during which they unloaded lots of new details on the upcoming expansion, which is shaping up to be a lot more fulfilling than the previous one (Chains of Promathia). Aht Urhgan will introduce several new aspects to gameplay such as Chocobo breeding/racing, Mog Lockers (pay-for-extra-inventory service), a Colosseum for Enemy vs. Enemy fights (for fun and perhaps for betting), new summons, and a Besieged mode where the new city of Al Zahbi will be attacked by beastmen and anyone in the vicinity with a weapon is required to defend several key points. Perhaps most exciting of all is the addition of a third new job, Puppetmaster. Below is a screenshot:
Also in the mix is a large number of proposed changes to jobs and other existing elements which may or may not actually be implemented upon release. Most of the content will be released in spurts throughout the remainder of the year, so even though the expansion comes out next month, don't expect it all to show up at once. Square-Enix's content release schedule indicated there would be additions all the way through December of 2006.