The background parallax looks strange, especially when there are doors. The doors also cover up the smoke effects and aiming lines, which feels and looks a bit weird.
The fact the hub is non-linear is cool, but it's hindered a bit by the fact that you basically pick levels at random, and you have no incentive to play all of them once you have enough keys to progress.
You also have no insight on what is within the level before you select it, so you're essentially picking stages at random until you get enough keys. This works in other games where the hub is presented as a map with branching paths, because it somehow makes deciding which path you pick feel more meaningful, and some levels are locked behind others. Maybe some levels could give out multiple keys? Or maybe the hub itself could be more interesting or complex to navigate, to make picking and choosing levels more interesting? Maybe certain levels could unlock keys to other areas of the hub? Dunno, just throwing out some ideas off the top of my head.
The tutorial introduced a pipe as the solution to the level, and I made a mental note that this would be the objective of the game throughout, but it turned out not to be true, even though pipes appeared later on in stages.
I think the movement feels good, jumping feels nice. But there is a weird gap between pressing the throw button and the player character actually beginning their wind up. This makes initiating a throw feel really awkward.
I think it actually plays quite nicely on mouse and keyboard, but the default controls need a little work - the less I have to move my hand all over the keyboard, the better.
The visuals are nice. I like the facial expression on the character when you aim, If you wanted to expand on that, the magnet's expression could change while it is in mid-air (it might already, but it's kind of hard to tell?), and also immediately after a collision. Maybe on the anticipation before the throw as well. The colour palette is good.
This is a bit of a weird one - technically returning to the hub being in the main menu makes sense, but for some reason it felt kinda weird.
Great job! love the video series. I hope my feedback is useful!