I really liked the demo. The puzzles were difficult enough to maintain me entertained, but not too much to be frustrating.
The game next demo definitely needs some sound effects, specially for secondary feedback of things happening in the level, like magnet changing polarity, or platforms moving.
In the hub, it feels weird how the background moves a different speed than the gates (that one would think that are in the same depth as the background)
Also, I would change the way the trow button works. Because for a short demo it's no such big deal, but for a full release game, it would be annoying how you have to maintain pressed the trow button to see the path of the magnet.
The other thing I don't like, is how the "double state buttons" (or levers) works. It doesn't always change to the side I like, or it is difficult to trow the magnet specifically to one half of the button.
What I really liked is the feel of the magnet. It feels heavy, but with powerful attraction at the same time. Also, the movement feels great, i had to habituate to the "long" delay making the biggest jumps, but once learned, i really liked it.
I hope this feedback helps you in some way.