I tried recording my reaction to stuff in the demo but I forgot to turn on my mic. Oh well, here's a summary of what I think could be improved,
1. Maybe try telling the player that you CAN change stuff like making matching colors go together.
2. Number the levels both in the hub and the levels themselves so you can easily tell which one's which.
3. The parallax in the hub makes no sense, if it's supposed to be a wall, then why do the doors not move with it?
4. The parallax background isn't even consistent! It seems like it's ONLY the hub that has it.
5. Occasionally when there's a ladder of platforms the platforms are just slightly far enough away that it seems like doing the smallest jump works, but it doesn't.
6. There's a "Return to Hub" button on the pause menu in the hub.
7. The only way to return the the hub from a level is to go into the pause menu and click "Return to Hub".
8. The particle effect go behind the doors and stuff in the hub
9. Realizing that the levels have names is not easy
10. In the level "Weight and Pull-me" it does not look like the magnet can be pulled up from the.... drill... platform?
11. You can cheese Blocked by Block with a strategy I show in this video. Don't be fooled, that took multiple attempts. Also that can probably be fixed by raising the button a bit relative to the other ground.
12. You can't move while getting ready to throw the magnet which feels very weird. And yet for some reason you can jump while getting ready to throw the magnet?13. This weird glitch in the surprisingly large "Thanks for playing" room.
I didn't notice it when recording that video, but even the text is affected by this glitch.That's all, hope you can fix/improve these things!