Man, that was really fun. From the title screen, you're already getting a player to figure things out, which is pretty cool. Got the final challenge on the first try (by pure luck of course)!
Regarding some of your questions:
1) What if you had some sort of ice cube that would melt in the right condition. Or possibly an object that explodes on collision.
2) I think it would be great to see a visual version of the transform controls. I know that probably would have been a lot of extra stuff for a jam, but being able to drag a rotation and scale would simplify controls a bit I think.
3) Every round, you introduced a new dynamic or challenge to the game. I think if you were to expand upon this, I would give a little breathing room between each new challenge introduced by having a second challenge similar in components to the previous. That also breaks up some of the tutorial text.