It's a really cool ambient experience... I love how light was handled in the game. And I love the little story that was told throughout!
The puzzle mechanics were a little confusing to me... I understand the idea of "some things only exist in the dark, while other things only exist in the light", which to me implies that only things you can see are tangible. Yet, there were levels with invisible walls that you bumped into in the dark. It was cool for revealing story stuff, but the puzzle elements got weaker as a result of the inconsistencies.
The platforming mechanics felt a bit sticky to me as well.
The way the story ended was a really cool wraparound!