Still not sure what I think about the aliens being some kind of "bio weapon." While the idea of them as soulless, engineered killing machines does still make them seem fairly ominous and terrifying.... I think I kinda prefer them as just mysterious creatures from some dark, unholy, nightmarish world in the far depths of space.
At the very least, I hope we don't have to see them actually being created in a lab or something. I think that really WOULD remove too much of the mystery.