Really cool and atmospheric demo, the audio design is a really awesome. It seems like it could lead to a really interesting game. The art is awesome and assists the atmosphere a lot.
I really loved the underwater section because it's setup so that you really believe that you're not going to make and raises the tension a lot. Also the fact that the time you have left is represented by the screen tinting blue is a very clever way of doing it instead of using a progress bar. All around great demo.
I initially thought the spikes would harm me and wasn't clear on how to make it past one point. Maybe changing the color to something less dark would make it clear that they are part of the background and not a game mechanic. Also I had some bugs with the rope but that was about it!
Really awesome job!