Neogaf forums leaked the folloing details about Mass Effect 2 :
You will play as Shepard, but for how long is unknown at this time
There is a new species called the Drell and Thane is a new character who is an assassin and may join your party
Planets – There will be a Krogan planet, and Illium, an Asari planet, that is like Coruscant from SW. Also there is ?Omega? with is like an anti-Citadel in that it?s huge and it?s the bottom of the barrel whereas the Citadel is the height of civilization. Also a Cerebus mothership will act as a location of significance.
Story – The ultimate story is still civilization fending off the Reapers, but this chapter will deal with this Cerebus corporation and it?s enigmatic leader.There are human civilizations disappearing and it?s up to Shepard to investigate, it?s termed as a ?suicide mission? which may lead to the details of the teaser.
New vehicle that controls better than the Mako?a ?new? control scheme.
Totally new and improved inventory system
Elevator system revamped where you will get the sense of scope of where you?re at and where you?re traveling.
No more texture pop ins.
Secondary races like Volus and Elcor are much more mobile, giving more depth and makes things more interesting.
Choices are more meaningful and there is a real risk that major support characters (i.e. anyone not Shepard) can and will die.
Also on the story, they?re super-hyping the ending, saying that it?s much more grand meaningful in ME2. More weapons, more species, more/new team members, returning team members, locations, weapons.