I love it! It feels great, the puzzles are fun to figure out, and I didn't notice any major issues. I really enjoyed myself!
Though there are a few things that need tweaking.
1. We should automatically pickup the magnet when we pass over it (unless we've just thrown it down where we're standing). Having to click or press E to grab it is unnecessary and feels like a chore because if I'm next to the magnet, I'm only ever there to grab it. If we really want to avoid grabbing it (which is rare), we can just jump over it (or walk under it if it's stuck to something).
The most used functions should be the easiest to activate, automatic if possible.
2. Collecting keys to unlock doors makes sense, however. None of the doors look like they use keys, and to open the door you... throw the magnet away? The mechanism of the doors themselves and how they are opened just doesn't make much sense. Perhaps if you collected keyCARDS, that would match with the aesthetic, and the doors would unlock (visually show that the key activated) automatically when you pass in from of them, and you have to choose to go inside them by pressing up for them to open and the level to start. Just default platformer standards.
3. The jump isn't high enough. The jump feels great! I love it! But since this isn't a platformer, the jump shouldn't require any skill to use for basic traversal. This includes needing to hold it down all the way just to get over a small hurdle. This game isn't about being good at jumping, even minimally.
4. Perhaps choose a different button for switching polarity? I sometimes want to switch polarity while moving right at the same time. With my index on D, hitting F doesn't feel right. Perhaps S? Or shift? Or even right click? Those don't currently serve a purpose. Choosing good default controls is important.
5. Maybe have the restart button not be CTRL? ENTER maybe? Also have it visually fill up/rotate/load in some way to show that you have to hold it.
Suggested future additions when making the full game:
1. Themes and decorations. Different color doors for different levels, different aesthetics/colors/textures in the floor, background, and decorations (when you add them). Give visual variety to the game. And when you keep the same theme for a group of levels, make sure the doors are still visually differentiated somehow (small images of the level layout, different decorations or icons for each door, big numbers on each door, etc. Up to you).
Who knows, perhaps the themes you choose can help dictate the "story" of the game whenever you get around the that part.
2. More character (facial expressions) for the robot.
Besides that, this game is turning out fantastic!
The puzzles are smooth and make sense, they escalate really well, and introduce the mechanics well. I definitely had a few "Aha!" moments.
The character feels great to control and move around (with the above noted exceptions).
This really feels like it's coming together, and I'm excited to see where you take it next!