This is an excellent submission! the mechanics are superb, with a good progression and the minimal art and sound combine very well!
My only comments are quite small, and could be easily fixed if you want to do an iteration of this magnificent game: is that the interface is a bit hard to read, its 2 modes having sometimes overlapping, and that there are some game breaking bugs when you drop elements (for me, the r for reset was not working and i was forced to drop the core, and at some point the level did not stop, and was unable to continue).
If you want, you should push this a bit further, it is an excellent base for a game.