Thanks for your feedback, I'm glad you like my game, even more so you're a puzzle professional!
I had footsteps in mind and did a few recordings, but I was not satisfied with them (too much background noise outside). As I deemed them to be the least important, they got cut. Is there something in particular you don't like about the death sounds? Maybe I can tweak them or redo them completely. Thanks for the pitching suggestion, that one's easily done.
About the move speed I pondered a lot. Although I agree movement is a bit slow, visually a notably faster movement felt a bit odd. I might further look into it and see if it's just the animation. Or, should I expand the game, I might add an option to set the movement speed to your liking as currently timing is not of the essence.
Regarding difficulty: the levels I included are meant as a tutorial, and even so they are my test audience was pleased by the amount of brain teasing. Further levels would have a rising difficulty, though with the current set of mechanics I think there's not much more to do aside from presenting larger levels with more of everything and adding dead ends as a distraction.
Or am I missing here something? Can you think of harder puzzles possible with the current set of elements? For me coming up with the last level had been already a challenge, but I don't have real experience in designing puzzles yet. So if you have any design ideas that would be more interesting to play for you, please share!
Thanks again, I'm happy to get a review from the target audience!