Halo Wars will rock the world. Best RTS on a console ever.
As for PJ and Bungie, they first announced the project at X06 over a year ago. It's an episodic series of interactive cinema with parts that are semi-playable. It will probably by half the price of a normal game and might only be available through download. My guess is it has something to due with the covenant, most likely the Elites.
Currently Playing:
Xbox 360 - Rock Band, NHL 08, Skate, Halo 3, Mass Effect
Wii - Mario Galaxy