Hey Salkafar , I am not sure if this is all due to a misunderstanding or if you just found huge problems with the entire movie, but I can respond to your points.
he doesn't say "This galactic system has a sun", he says "This galactic system has a sun a lot like ours", the point of his sentence being that the sun is a lot like ours, not that it has a sun and that makes it like our system.
because let's face it, if he had said that it would be monumentally stupid, so it couldn't have possibly meant that. I guess i can agree, his timing may have been problematic in order for anybody to misunderstand in that way. an acting weakness perhaps?
the womans stomach wall etc, I can see that being an issue if we expect the director to hold our hand through the entire movie. I find it a very good point that Ridley Scott respects us enough that he didn't need to outright say that this is advanced medical technology and that the multiple injections she was giving herself have no doubt had some effect to bolster her body systems and aid accelerated healing. I thought it was left very open to interpretation, but the fact she was running around after major surgery led me to believe that there was some advanced regenerative medicine at work.
the fact the engineers changed their plans... I think this was far more than a simple rash decision due to the failure of one ship, I think that experiments like these may have led to heavy political debating among their society but the fact is we just don't know, we aren't given anywhere near enough information to formulate any assumptions.
I can't personally accept the description of it as a 'dumb flick' right now. I've seen it twice and i still love it. of course I'd love to hear some more of your views.