Moving the character is very fun. I liked how throwing the magnet mid-air happens instantly. I also appreciated how the permanent switches actually looked like literal switches, and the pressure plates looked flat.
FYI: I tried to replay the levels, and it would let me enter them but not complete them since the keys were already collected. Probably something you already planned to fix in a final version, but I thought I would mention it.
My only real criticisms of the gameplay have to do with a couple unintuitive inconsistencies. One was the pass-through platforms/walls that for some reason allow the magnet to pass through, but not the robot. It felt especially weird when they were platforms because you would expect objects to land on platforms the same way the player character does. Once you understand this it's not hard to adjust, but it is odd.
The other inconsistency I noticed was the way the robot holds on to the magnet when being pulled up by a vertical magnetic field but lets go when it's a horizontal field like the L-shaped doors. Seems like it should always hold on since we have the option to throw.