Wow, I loved this! I love the art style and music. The puzzles, storytelling, and, atmosphere are well thought-out and immersive. The puzzles themselves started fairly simple but can get a bit challenging, although nothing you can't figure out if you look around. I found it very calming and charming, the type of game you can sink into your chair and relax to.
As far as things to improve, all minor, one bug is that if you drop a lighted cube in the apse when the shutters are closed, you can't retrieve it back and have to reload. The game is also fairly short -- I finished it in an hour. More puzzles/longer playing time and I think it can be a good Steam game. Lastly, make this page/layout look better so more people play this game :)