Many other posters have described just how bad it is so I won't bother recapping things. Just accept it -- it's really, really bad.
But... it's so bad that it's funny in a Mystery Science Theatre 3000 sort of way. You just have to sit back and try to imagine which direction the next silly plot fork will go. Will the family really be stupid enough to do what the plot is leading them towards, or will they show some rare sign of above-70-IQ intelligence? Oh, it looks like the "smart" daughter is going to say something... how many different physical laws will her pronouncement violate? Oh boy, a big nasty is coming towards "mom"... will she waste it, reason with it, or run away. It really doesn't matter what happens, the chances are good that it will make no sense and lead to laughter along the lines of, "Who gave these people money to make this?" and "Maybe I can get in on the gravy train?"
But... it's so bad that it's funny in a Mystery Science Theatre 3000 sort of way. You just have to sit back and try to imagine which direction the next silly plot fork will go. Will the family really be stupid enough to do what the plot is leading them towards, or will they show some rare sign of above-70-IQ intelligence? Oh, it looks like the "smart" daughter is going to say something... how many different physical laws will her pronouncement violate? Oh boy, a big nasty is coming towards "mom"... will she waste it, reason with it, or run away. It really doesn't matter what happens, the chances are good that it will make no sense and lead to laughter along the lines of, "Who gave these people money to make this?" and "Maybe I can get in on the gravy train?"