The characters in Blade Runner have very little detail attached to them but what we do see rings true.
For me there is nothing in the film that I have to let pass.
The characters in Prometheus (David being the possible exception but some of his scenes are scuppered by the rest of the crew) make no sense but nonsense.
What I meant by comparing the creatures in this film to the alien life cycle is in the 1979 film they made narrative sense to be the way they were in that film.
In this film they are just less interesting stand-ins for we have already seen but they are only there because the actors need some object to respond to, there is no narrative requirement for them to be the way they are, they could have looked like anything and acted in any way.
The problem for me isn't that it isn't a straight Alien prequel (though with the current story elements that would make more sense) rather it's too much like a straight Alien prequel only with the alien replaced by something a bit like the things in the Alien films only not as interesting.
They should have gone with the straight Alien prequel or written a totally new film this is the same half way watered down mishmash that Alien 3 (Ward's space monks plus Twohy's prison planet) was and it's not even as good a film as that.
Like the PT it's full of implausible characters doing stupid things in a story that doesn't make sense.
This is true even if you try to ignore it's not an Alien prequel which is a hard task because everyone is going through such hoops to remind me it is one.