Do you remember the vrykul, those Norse-themed warriors you fought in Northrend? Well, Halls of Valor is a fortress in the sky above Stormheim where the greatest of the vrykul warriors go after death. There's a good reason for players to disrupt their little Valhalla, though. God-King Skovald and his forces have invaded the hall to recover a powerful artifact for the Burning Legion that will help them take over Azeroth.
There are five bosses through the Halls of Valor. In addition to fighting Skovald and his minions, players will also face down the Titan Odyn, who has fallen victim to a cursed. Blizzard also included a fight against a giant wolf in there for good measure. Here's the dungeon journal description of each boss (via MMO Champion):
Hymdall - "Having proved himself in honorable battle, Odyn tasked Hymdall to guard the entrance to the Halls of Valor. Hymdall has stood, never erring, in this watch protecting these halls from all dangers."
Hyrja - "In life Hyrja was a warrior without equal, defending the Valkira from all threats. Her valor and courage drew the attention of Eyir, a titan watcher. Upon her death and ascension to the Halls of Valor Eyir has awarded Hyrja with her greatest honor, transformation into a Val'kyr."
Fenryr - "Fenryr has eluded even the best hunters of the Halls of Valor."
God-King Skovald - "Gul'dan approached Skovald with a proposition, have his vrykul join the Legion or see his people be destroyed. With the promise of 1,000's of worlds to conquer Skovald has taken up the Legion's offer. Before being allowed to fully enter the ranks of the Burning Legion he must first secure the Aegis of Aggramar from Odyn's realm of the Halls of Valor only then can his endless conquest begin."
Odyn - "Odyn, a titan keeper, forged the Halls of Valor to house the souls of the greatest vrykul warriors. These warriors have been forged into a new army, the valarjar, in order protect Azeroth from all threats. However, cursed by Helya, Odyn and his army are now trapped within these halls."
The last fight looks like a lot of fun. Players are tagged with colored brands that damage them over time and they have to run to the corresponding tile on the ground to remove the effect. Doing so turns the player into a Val'kyr (ie a giant viking angel thing) for a little while and gives them a huge boost to healing and damage. You'll need that buff because Odyn is constantly tossing Holy damage around and summoning minions.
Legion's alpha test launched about a week ago. It's mostly limited to friends and family of Blizzard employees. Those lucky few are able to try out small chunks of the expansion pack including the new Demon Hunter class. Blizzard will follow up on this closed alpha with a larger beta test closer to the expansion's launch next year.