Obviously it contains some big spoilers and is best avoided if you’ve been keeping yourself under a narrative-free rock until it releases. The gameplay footage is rough and unpolished.
Again, avoid watching it if you don’t want anything spoiled. The first part has Commander Shephard and Captain Anderson on Earth during the initial Reaper assault.
The second part has Shepard, Garrus and Liara escorting Mordin and a Krogan vital to the main story, with Wrex not to far away. The gameplay is a rough glimpse of Mass Effect 3 and so there’s little doubt it came from the leaked beta version over Xbox Live. Mass Effect 3 releases on Xbox 360, PS3 and PC March 6th in the US, 9th in Europe.