Jason Borne is supposed to be like that.
Angelina Jolie's character in Salt is supposed to be like that.
There are many soldier/assassin type characters who are supposed to be cold and emotionless who still bring an energy to the role.
I found that Brie brought no energy. She was not just robotic and emotionless, she was flat. There is a big difference.
Watch Rich Franklin play cyborg soldier
and compare that to Arnie playing the Terminator, or another cyborg soldier and see how Rich in trying to be robotic and emotionless is just completely flat and lifeless.
Arnie breaths life in the role because he brings a energy and can act.
I am not saying Brie cannot act, but i am not sure she did much of that, in her first movie.