Pretty good, one minor annoyance is that the non polarized switch doors have a "cooldown" which means if I try to go through one and then immediately turn back I get stuck running against them and have to turn back and then push against them again. Noticed that immediately with the first door.
Puzzles felt honestly a bit easy and most of the time there isn't even really a way to do things that don't progress towards solving the puzzle so you could solve it accidentaly.
Last puzzle on the other hand was super frustrating. I kept messing up the throw and the timing and angle to change the polarity is relatively precise considering you have to then run quickly otherwise the block squishes you, I had the solution and kept failing for a while because I didn't succeed to apply it and that was really annoying. Another major annoyance was that the button was too far from the wall so even when the throw was successful the magnet sometimes got stuck behind the button without actually pressing it. The jump is also super tight and I had to reset multiple times because I got my magnet stuck on the other side and failed the jump. Overall a very unfun level for me and I was disappointed that it was the final level too since I expected a last more intricate level once I unlocked the final door. I get this is a demo but getting a thanks for playing when you prepare for a final challenge is a bit of a letdown especially when you come out of a very frustrating level =p