It feels like you're on the road to a very good game but still have some way to go. The most impressive thing about this is the presentation which gives a very moody and calming atmosphere in a very simple and understated way.
The worst aspect, for me, was the level design which required repetitive jumping onto nearly identical featureless rocks. As well as the breakneck plummeting- which you mentioned- not knowing where the platforms below you were was also an issue (in pro games like Mario, these tend to be placed in a fair way, or give you a hint so you're not falling blind).
The cut scenes were very well done though and the story was quite sweet in the end- I was wondering if it was going to turn into a Silent Hill style emotional pain game at one point! As Rainy G mentioned, doing more to marry the story to the gameplay would be really cool.