It's been suggested many times that the aliens don't know what water
is, hence coming to Earth and not knowing that most of what Earth is made of will kill them. The criticism from the movie comes from people who only understand simple science - that ALL life
must have water in the vast infinite universe. The possibility that this is a species that isn't comprised of water and never came into contact with it is too much for people. The other argument of condensation and water vapors having to kill them, because water is in our air at all times -- again, it's not stated in the movie that this doesn't
harm them. It might make them sick or weak, hence why the one alien can't escape the pantry.
As for not knowing what a doorknob is and how to turn it, I don't understand the argument... Are they supposed to know what doors and doorknobs are in their home galaxy? Why is it assumed that they're vastly more intelligent than us on EVERYTHING and NOT just on the things that they understand from their home?
I mean, I just don't get why any of this needed to be fully explained. That would require whole paragraphs of dialogue like above. And then people would be complaining about the exposition.