Why the low rating???

Because it just wasn't that great. It was well done for having such a low budget and the performances and effects were decent enough, but in the end it just wasn't a very entertaining or memorable story. A whole lot of exposition and not much actual content. I wouldn't really classify it as a bad movie, but it wasn't satisfying either and I would never watch it again by choice.

For a horror film it certainly is one of the better ones out there.
I agree it should get a higher rating.

Also one other thing I can comment on is the actor portraying the German officer.
He sounds amazingly like Christopher Lee.

Maybe this world is another planet's Hell. - Aldous Huxley (1894-1963)

he's being seduced by a shape-shifting demon and the shots are from the neck up? Fail