This 2 minute clip came from a Bioware presentation at GDC about the development of Mass Effect 2. The gameplay is at a very, very pre-alpha stage.
No spoilers per se, and the shakycam makes it hard to take in any visual differences. If you listen closely you might be able to piece together one of the missions - sounds like you have to stop an intergalactic hitman in the middle of his next job.
Anyway, it doesn't give up enough to really be a teaser, but it is interesting to see how the team blocks out a game's development and then fills it in.
Mass Effect 2 Leaked Gameplay GDC09 [Gametrailers]