Love the art style! City in the back looks beautiful. Gameplay background is awesome, without taking too much attention from the foreground. How did you make the grid? Is it a tilemap?
Gameplay is very unique, you could definitely add more levels with some additional mechanics. Sometimes it was hard to set the height precisely, some control acceleration could maybe help there.
I have only noticed that hearts appear on buildings after 3rd building, it would be awesome if the animation was more flashy, maybe with some sound effect to accompany. But the game is great as is, mood is wonderful.