This movie has the most real people that I've ever seen in a movie. They are not polished, they don't have special skills that will make them better able to defeat the threat and they don't have archetypal flaws that can be exploited. The characters are just people who happen to be there at the time. The film really makes you believe that this could happen to you, that the whole world could change and go completely crazy and that you could be left with an imminent threat of individual extinction. It wasn't really a directly terrifying film, but I think that it's one of those things that will sit in the back of your mind and bother you for the rest of your life. That's how Tremors was for me. The film isn't scary at all (I didn't even find it so as a child) and at times it was even funny, but to this day I sometimes still find myself rushing across open ground so that I won't be caught there.
Invasion also has some very interesting camera angles and monster make up. It went along w/ the theme of the film that everything could appear completely normal, but there is just something a little off about it. There is one point when Donald Sutherland's character is coming through this doorway. His sticks his head through first to make sure that there isn't anybody on the other side. The camera angle makes is such that he looks, at first, like he's coming up through a trapdoor. But, he's really just coming through a regular doorway. At another point, Lennard Nemoy's (sp?) character is walking to his car. Behind him the street must be on a hill or something like that because it's tilted relative to his body. As the camera follows him, you can't really tell that it's a hill (at least I couldn't) until he reaches his car and you can see that his side of the street is level relative to his body. The make up during the growth of the podpeople is cool too. They start out looking very fetal and covered w/ this grey hair. Then they gradually come to look exactly like the people that they are copying. The details are exact, right down to a bloody nose, a scar, or a pompous mustache.
One thing that I did not like about this film is that the group kept trusting people, even after they realized that people were being exactly duplicated. I wouldn't trust anyone that I hadn't been w/ the entire time. That just doesn't make sense to me.
I also didn't like that the whole helpless female heroine thing that they had going on. It was more subtle than in other films, but it was still there.
An interesting point that they made at the end of the film was to follow Donald Sutherland's character around during his daily routine. At this point you can't tell whether he is a podperson or whether he is just pretending to be one. Don't worry, I won't give it away. But, the point is that life is pretty much how it always was. Except that there was no crime or pain or war. There was also no love. The podpeople said that they had the same memories that the original person did. Did the original people really die? Or, were do they still exist, but in a different form?