Finally, a teaser trailer that actually teased. Seems the story might be very interesting - if Shepard is believed to be dead (and obviously makes a comeback), might we be playing someone else in the meantime? Or perhaps we're always playing Shepard, but while undercover or something similar. Or maybe we never play Shepard at all, and he's an NPC in the game (a very powerful one).
From the video it did seem like the player was controlling Shepard though, so unless told otherwise by BW, I will assume Shepard is the main character of ME2 as well, though it will be interesting to see how they're going to "reset" him/her - there's no way we get to play a level 60 Shepard, as the level of power Shepard reaches by level 60 is simply redicilous (especially the amount of crowd control it is possible to get - there's no way to "scale" enemies to be difficult either, since they're usually just floating around in the air when they're fighting a high level biotic).