Some players are in an uproar over the fact that the special Digital Deluxe edition of Mass Effect 3 will be limited as an Origin exclusive.
Unless Valve does something in retaliation, players will likely still be able to purchase the game on Steam, but doing so will disallow you access to the game's limited N7 Arsenal Pack, Squadmate Alternate Outfit Pack, and Robotic Dog.
Mass Effect 3 will be released some time in 2012.
