This is 10 minutes of beautiful atmospheric filmmaking on all fronts. As a proof of concept short, I loved it. It is a nice horror short on its own, and I would love to see a full length feature version.
Visually, this horror short is top notch. It has a great dark and eerie vibe like most good horror stories should, and the beautiful lighting in this film sets the mood just right. The tension building throughout the film is great as well, as it keeps a great sense of mystery contained, letting the viewer use their imagination. If I had one complaint, I would probably say the pinkish/magenta colored light used as a representation of sinister value was probably not the best choice; regardless, it definitely did NOT have a negative impact on the quality of the film.
As a horror fan, I think Who's There has teeth, and I like to be bitten, so someone give this man what he needs to make the feature a reality.
Knock Knock!