The characters and levels have a good feel. Something very satisfying about the way the robots' wheel turns, especially when he's on hanging from his magnet.
I really enjoyed the last two levels. They were frustrating at first but it was very fun to have that sudden realisation that makes the whole thing come together and allows you to sail back to get the key.
When you do bring in sound design etc, it will be important to make it very satisfying to pick up a key (in the same way that its satisfying to get an item from a chest in Ocarania of Time) as the player sometimes has to work quite hard to get it.
I had two main challenges.
Number 1 - At first, I kept throwing the magnet when I meant to pick it up, for some reason I just hold down the E key to pick up the magnet. I then find that I'm in the throwing mechanic, and there doesn't seem to be a way to cancel out of that.
Number 2 - There were lots of times when I had to restart a level because I was stuck. This didn't feel too bad as the levels are quite short. That meant it didn't feel like a drag to get back to where I was. Would be more of a problem if it happened on a longer level, though.