I loved the Demo. The game is really interesting, the art is good, and the sounds really give the user a horror atmosphere. The controls are simple and nice to manage, as well.
My biggest complaint is that areas get closed off and it doesn't really feel like you actually completed them. Which is a problem: most gamers want to complete and explore everything before moving on. So I think some dead space could be cut. Or maybe somehow make it clearer (not through words) that you don't have to visit every item.
For example, i didn't have a problem with the first puzzle, but I actually had to think "oh so these other cardboard boxes are just dead ends and should be ignored, and so should the previous tunnels.
Then with the second puzzle (getting the mouse), I just happened to explore pick the right "rune" to jump down at to immediately get the mouse, so I didn't end up needing to explore, even though it felt like I had missed out on a lot.
I also think there needs to be some more emphasis that you complete a puzzle or that you moved on in the game. Even though I completed the entire demo, it just felt like one long continuous sequence. Giving the game a little more feeling between saves/parts would make it even better.
That said, I really like the game and will definitely play it. Nice job. 5/5.