There are some really cool puzzles in here, especially towards the end! It's really hard to design space-efficient, claustrophobic levels so that they pose a specific problem/concept, but your game is really nailing that.
I don't know if you've played much with Stephen Lavelle's puzzlescript engine, but one really neat feature it has is that the undo stack includes level restarts. With these sorts of puzzles, sometimes you think you've dead-ended yourself, restart and then have a eureka moment and realise you were on the right track after all, and that's where undoing restarts is a blessing :)