Great example of how a simple game (not in a bad way) can keep you hooked. Loved the exploration, the mechanics, the little notes and the puzzles themselves of course. :) There are 2 small things I'd recommend:
1. The floor tiles blend a little bit too well with the walls and other non-walkable areas so it was hard to tell sometimes where I can or cannot go. A different color or maybe a darker shade would make it more "readable" I think.
2. When you finish a level, I'd add a little popup for a few seconds that says "Level 2" or "Floor 2" to provide feedback to the player that they are progressing and this is now another level.
But these are just small tweaks to an otherwise fun little puzzle game. Good job!