An early build of Mass Effect 2 was shown to event goers at GDC 2009. Nothing much was revealed plot-wise, but the MTV Multiplayer Blog does share what they noticed in terms of changes in gameplay.
So far, it looks like the sequel is keeping things familiar while tweaking small things here and there for the better. We'll have more information on Mass Effect 2 as it is made available.
In the combat scene, the circular targeting reticule of the first “Mass Effect” appeared to be switched to crosshairs that expanded and contracted during combat, possibly due to the rapid firing of the character’s rapid-fire gun. The dialogue scene appeared to use the same mechanics as seen in the original game. It showed lots of cars flying through a city. The main character, a blonde man, was speaking with a blue alien woman.
So far, it looks like the sequel is keeping things familiar while tweaking small things here and there for the better. We'll have more information on Mass Effect 2 as it is made available.