Love the aesthetic! Substantial and varied puzzles. Really solid work!
A few things on my wishlist:
- some fanfare when collecting the key at the end of an area (large-scale animation/flash/particles + happy audio beeps)
- some talking characters + backstory (even if it's just fluff, I'd enjoy it and think it would help fill out the game-world)
Admittedly I'm taking a break midway through (it's late and my brain is too tired to push blocks) so I might have missed some things!