THIS GAME IS AWSOME!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
erm essentially what happened in the Arrival DLC was that Admiral Hackett requested a favor of you to rescue one of his friends a doctor who was being held at an Batarian prison for terrorism, you land on the planet, free her from the prison cell, you escape and she basically tells you that technically the charges weren't wrong, and that she along with a huge group of scientists were planning to send a meteorite through a Mass Relay blowing it up, but in the process killing thousands of batarians on the system, however she states that it's necassary because the Reapers are planning on using that relay as a short cut to the Milky Way, you go to the meteorite where a small station is there along the way, you find out that the artifact that they discovered that gave them the vision of the invasion, is now indoctrinating them, long story short they try to stop you, they fail epically and you destroy a batarian system, however delaying the reaper invasion, thats what the 'shit' Anderson was talking about and thats why you were temporarily disbarred from the Alliance.
No offense against ME fans, but from what I've seen of ME I think Gears of War is a better story and over all game series, but that's just my opinion don't mean to ruffle any feathers.