I love small out-of-the-box thinking puzzle games. My favorites are ones where you can just manipulate things until you figure out what you're supposed to do. The 3rd and 4th puzzles follow this a bit so were my favorites. I'm not sure how long it would have taken me to figure out the 5th puzzle without the hint, but it made clear sense after solving it! I'm still not sure why the solution to the 6th puzzle is what it is though.
I think my biggest complaint/critique would be regarding how you control the game/manipulate objects. I don't think pushing with a cursor that moves based on where you clicked feels the greatest to use. It's a bit too slow and clunky at times. I would have preferred a click and drag objects.
Great job on making the game, and I would love to see more puzzles/levels!