It's very atmospheric and eerie, and a bit like watching a dream.
There's an article in Wikipedia
http://en.wikipedia.org/wiki/Vampyr
and the full film here: (about 70 minutes)
Dreyer reportedly told his cameraman, "Imagine we are sitting in an ordinary room. Suddenly we are told that there is a corpse behind the door. In an instant, the room we are sitting in is completely altered: everything in it has taken on another level; the light, the atmosphere have changed, though they are physically the same. This is because we have changed... This is the effect I want to get."
