It will probably end up being a 'Sleeper hit' ( an exact number? I dont know) but you never know, because Minecraft became popular by word of mouth alone, and look how many people have bought that game, and its not even out of Beta stage yet!
This. Minecraft is techincally not even released, and it's recently gotten
two million purchases. The entire time, it's spread only by word of mouth, and word of text.
BRINK will do very well, Methinks. Maybe not enough to topple the amount of sales Portal 2 has, but enough to stabilize itself as a new franchise.