I don't think that I've ever seen such a unique game mechanic before. That added with the nice upbeat music(especially when falling down a well), really creates a nice atmosphere.
Biggest problem though, is the movement itself. It feels off, and hard to say how far you'll go. I would suggest adding a breath meter to see you much oxygen you've breathed in.
I believe that if you make some tweaks and adjustments, you could have an amazing game! Nether the les, congrats on your game! :)