BioWare's Casey Hudson has been interviewed at 360.IGN about Mass Effect. Here's a snip:
More information.IGN: So you just spoke about how you want players to feel that they're somebody special. We know that you take the role of Commander Shepard as the main character and I've read that you can create your own character and build him from the ground up. How do you manage to make this game where the two ideas co-exist, where you can create your own character and build your own persona and still fit him into this world and story where he is special?
Casey Hudson: Well it's an interesting balance and I think it's a different balance than anyone has ever done before in a role-playing game. I think typically role-playing games in the past have been more about creating a completely empty vessel that you then fill up with whatever choices that you make. And that can be really cool but it also kind of leaves out a little bit of the texture of what it's like to be someone specific or to have a specific spirit to an adventure.
So if you think about some of the really great, memorable science fiction stories or even characters, like Captain Kirk or Jack Bauer. Any story about that kind of a character has a very specific flavor to it and that's one thing we didn't want to miss out on with Mass Effect. Mass Effect is so much more cinematic and real than anything we've ever done before that we really needed that extra bit, those extra sensory aspects to a story that you can't get if you just start out with a completely blank character.