I loved the flashbacks - the interesting part was that there was not too much guessing when Sinatra's character realizes that he must have been hypnotized while imprisoned. The mental adaptation were adapted by the different soldiers in personal ways - it adds bizarre humor to the story. The characters were strongly identifiable and everybody did quite an amazing job with acting - especially the mother is so evil just on the brink of overdoing it, but her performance worked fantastically well.
The added revelation about her character in the end was maybe just a tiny bit too far-fetched. But it didn't matter I was willingly suspending my disbelief. The showdown is also quite fantastic in the way the spatial geometry of the hall is translated into a cunningly edited sequence of locations inside the building when Sinatra tries to find his way to the man.
Some impressive camerawork using unfocused foreground in relation to the background.