Nice game! It was enjoyable to play and I almost managed to beat your highscore. I think I have to try again after some sleep.
The concept fit the theme nicely and flipping the polarity of the ship shield to prevent being hit was fun mechanic. To make the magnetism aspect to be even more involved in the gameplay the magnetic forces could be even higher. Then having blue shield would also attract red bullets which now didn't really feel like the case.
The visuals are also nice. I especially like the player ship with the different shields and moving background stars. There was no audio at least at the time when I was testing this.
One thing that surprised me as a player was that the enemy ships were never destroyed no matter how many bullets I shot at them. I would have liked to be able to destroy the enemy ships to feel that I'm making progress in the game. I think this would make the game much more enjoyable! Now it felt that I was just shooting around and got points all the time.
It was a bit unclear to me does the player ship have any health? Maybe you could consider adding some visuals for that: a HP bar or heart/shield symbols somewhere on the screen to represent how much health the player still has.