Hello, I played your demo and it was quite fun! Completed it under 10 minutes or so.
What I enjoyed:
I loved some of these puzzles in their simplicity. Not to say that they didn't require thought, because they did. I know the last puzzle had me going for a second.
I like being able to restart the level immediately by just pressing control.
The character design is quite nice and the whole thing is enjoyable to look at!
I am looking forward to the full game!
What could have been better:
I think it was often unclear how far and high you could jump, some jumps I felt like I could make that I couldn't and jumps I thought I couldn't make turned out to be the required path.
Something that I believe that is unintuitive is that like charges don't repel in the game. Everyone knows how magnets work, so people's first thought would be about repulsion and attraction!
I don't know if this is intentional or not, but when playing with a mouse going into aiming mode locks you from moving left and right and I think that being able to move and adjust would make this a lot less clunky.
The magnet doesn't seem to have much character. I suggest that the positive polarity have a really happy face and the negative having a sad face, it would just make the magnet feel a lot more alive and fun.
Possibly add a fun little idle animation while you are stuck on a puzzle and just thinking about it.
The lack of noise and music left me alone with my thoughts far too long, the creepy silence definitely added a little horror to the game but I don't think that was the intention as I know you haven't made the soundtrack yet.
Levels can feel a tad samey due to a lack of changing environments. Possibly as the game goes on, the levels progressively get more rundown or feature different sciencey stuff to show you going through a facility or something. To make it even more distinct, different worlds having different music and stuff.
Finally, I understand puzzle games aren't supposed to be stressful or timed experiences. However, I felt like the game was made more boring purely by the fact that there is nothing going against you at any point (other than your own stupidity of course, I faced that villain many times). Possibly having late game levels with rising lava/side scrolling, enemies, or timed things with a bomb.
My suggests are likely quite difficult to do and I am definitely not saying i could this, because I definitely couldn't, but I just thought this might be some helpful perspective from a long-time puzzle gamer. Thank you for giving this demo away for free, I enjoyed it very much.