Right now you're probably either scratching your head or saying 'really? Rakghouls?' If you've never played Knights of the Old Republic, then you're probably the former and don't have any idea what a Rakghoul is. Allow me:
The Rakghoul is the end result of a Sith bioweapon, turning beings into mindless mutants. Rakghoul infection can be transferred by contact with one. The original outbreak occurred on the planet Taris, where they plagued the inhabitants of the Undercity – criminals or their descendants – but they also live on Coruscant. First appeared in Star Wars: Knights of the Old Republic - From the Star Wars Wiki page
The expansion (update 1.1) launches next week (January 17th) and will have to tide players over until the following content pack goes live this March. That update hasn't even been hinted at yet but will include many of the same play elements of RotR, but with new locations and missions.
As for Rise of the Rakghouls- here's what you'll be downloading next week:
Rise of the Rakghouls features a new Flashpoint and a new Operation as well as a number of changes made throughout the entire game, including level 50 bracketing for PvP WarZones, the addition of anti-aliasing and changes to Open World PvP on Ilum.
- Flashpoint: Kaon Under Siege is a completely new and unique group combat experience located on Kaon, a planet in the Tion Hegemony, a strategically important sector of the galaxy that has remained neutral, Groups of up to four Republic or Imperial players must race to Kaon to eliminate the Rakghouls outbreak, securing the allegiance of the Tion Hegemony for their respective sides. This Flashpoint will be available for level 50 characters only and will feature Normal and Heroic modes.
- Operation: Karagga’s Palace, is a continuation of the game’s second launch Operation. In the Operation, teams of 8 or 16 players will face off against Karagga and the Hutt Cartel after the Hutts abandon their famous neutrality and breach agreements with both the Republic and Empire. Concerned by the threat of another combatant in the war for galactic control, both factions send teams of their most powerful heroes to confront Karagga and determine his intentions. This Operation will feature Normal, Heroic and Nightmare difficulty modes.