Really well designed levels!
However, it was really frustrating when I would screw up jumps and things (forcing me to keep retrying puzzles I knew what I had to do to solve) when my muscle memory kept trying to use the up arrow instead of X to jump. This is an easy fix: change 'jump' to up arrow and 'switch item' to X. Alternatively, offer a way to input controls (if that's possible with PICO, I'm not sure).
It's a testament to the great puzzle design that I didn't give up immediately when I ran into these issues, though. Overall, really great game, and I'd love to see more!