Great demo! The improvements in the way the character feels are great. Only thing that might be nice is if you could move slowly while aiming instead of having to cancel the throw and move if your just a little off. I also would like to be able to rebind the mouse buttons as personally I'd rather have right click be polarization.
I enjoyed all the puzzles and felt like the difficulty was good. The magnet feels very central to these levels so I think that has improved massively. Like other reviewers, I didn't immediately get the pipe and tried to jump in it, though i do really like it as a mechanic. Maybe some something to differentiate it from green mario pipes would stop players from trying to jump in it.
Only annoyance as far as mechanics is that with the rotating walls that the player can push, turning around too quickly to walk back through it can cause it to not open. This is only mildly annoying, but it does feel clunky if you realize you need to turn around. video here