You played the extended cut of ME3 and now you've been waiting for DLC which doesn't feature new weapon packs or other bullshit. You wanted more campaign, you heard about some rumours, got your hopes up and now you can be happy:
Reaper origins! I wonder how much of that DLC fits into the narrative offered by the extend cut. I bet Bioware has been painstaking in that regard... to make it make sense.
From the Bioware blog:
"Something lurks in the dark corners of space, something powerful enough to kill a Reaper. Shepard must discover the most closely guarded secret in the galaxy before the Reapers silence it forever. Discover more about the origins of the Reapers as you race across the galaxy to find the Leviathan. Unravel the dark history of the Reaper Race before it is too late. Coming later this summer there is no war, only the harvest."
We'll also get a chance to explore new parts of the Citadel.