On the plus side, I really liked the direction and I had fun playing the game once I figured out what I was supposed to do. Making blocks and seeing them slot together was very satisfying. The art direction was consistent, and I liked the almost whimsical tone of the game. It helps ease the player into the more serious themes.
The playable demo was a bit buggy though. The music stopped after a certain point, and when my tower reached the area where the blocks had been spawning from, the spawned block caused my tower to fall down even before I released it. One block even started floating in space. I'd recommend having either a sensor to check when the tower has reached a certain height, so that the height in which the block spawns from can be adjusted accordingly. I also was unsure what was meant to be the fuel blocks and what was meant to be the natural blocks, as I felt that both types seem to be easily stackable.
All in all, a good twist on a fun game mechanic and I loved the art.