Nice short but (mostly) challenging puzzles! Here's one probably obvious thing I've noticed right away - because I wanted to solve the first level faster:
1) When you replay an already completed level there's no way to exit it aside from using the menu. Maybe add a greyed out key (like the stars in Mario 64) to ensure replayability of levels ;)
2) And the default key bindings for right (D) and switching polarity (F) get in the way when switching and moving to the right at the same time or successively.