This is a beautiful story of the what ifs of an alien invasion that could go almost undetected and take us as we sleep.  Sleep no more, indeed.  A tale that is haunting and suspenseful the whole way through.  The slow change that comes over Dr. Bennell through the course of the movie from the early dismissals to the slow realization of the truth to the psychotic nature at the end is brilliantly portrayed.  The peripheral characters also are mostly believable in roles that could have them coming off very corny or over the top.  The cinematography is wonderful showing just enough while keeping some things hidden in shadows, or off the screen, or quickly removed.  The story itself is told outstandingly and surprisingly realistic, minus a couple gaffs which only add to the action and atmosphere for entertainment purposes, and mostly can be overlooked.  The beauty of the story is the idea behind it.  Would we notice changes in people if they still looked, acted, and were exactly the same minus the human emotion?  Would we fight for survival, or take the nap of destiny?  Not only is it a thriller, it can become a think piece.

  That's where the negatives come in.  The setup (which Hollywood, not Siegel wanted) involved a flashback storytelling of the film.  Therefore, some of the suspense is removed early knowing at least the doctor makes it far enough to tell the tale (though part of me was hoping that he was telling it too the invaders in the end).  Likewise, the Hollywood ending that was tacked on involved an optimistic outlook, while the original approach was open ended and pessimistic, which would have worked better in my opinion.  Those issues and some small story holes take this away from being a nearly perfect film.  Instead it is merely very very good.  9/10