Incredibly fun! A couple of things I would like to point out. I would like to be able to move while I'm aiming my magnet. Let's say I just entered a level and see a spot I could throw my magnet. In my excitement I run towards that spot and start aiming my magnet well before I get to that spot, now I find myself stuck and my first thought is to throw the magnet as the cancel button is not mentioned at all. Another thing is that when I entered the level selection, I would spawn all the way to the left, which kind of made me lose my sense of progress, as if that level meant nothing at all. I will admit I'm a bit dramatic, but it was still frustrating. That's all though, this demo was really fun, and I found myself entering each new level with joy.
edit: being able to move while aiming the magnet for the controller might not work out, you could use the right joystick but that would only be possible if you could toggle the aim mode instead of holding the button (which is a great idea honestly)