I always enjoy a game that's simple to grasp as a concept and proves to be difficult in execution. Your game is difficult in execution over a particular concept that I failed to recognize until I saw you mention it in a comment, and once I understood actually made it extremely easy to beat the game again (5 minutes instead of an 45): friction. Even with the word tip, I felt accomplished to be forced to try and find another way to play through to beat certain levels, and made it a more enjoyable experience.
My critique would be although once I learned how to do this (with the infamous empty level with the goal in the top right corner), I could actually do it to most of the other levels in the same design when I played again, and it felt like I was easily able to abuse the game play. Otherwise, this was a very atmospheric and worthwhile game. I feel if you're going to go with the concepts of depression and shadows, that you should elaborate and include more detail in an expansion or sequel, otherwise it's a bit too light to do anything with it.
Cheers, hope you do well in the contest.