That's how you make a low budget, period piece, sci-fi film!
Don't expect the traditional 'action' and 'vfx'. It's a DIFFERENT type of film. I think it is SO WELL DONE. I think it is masterful how they used so little and made it work so well.
High production quality, great pacing. In lesser hands this would've been a complete failure.
I would say it's not a horror film at all. There is suspense. Possibly one reason I loved it so much is that I also had lower expectations going into it, I didn't know exactly what to expect either.