Pros:
Fun art style. A lot done with very little. Post processing + soft lighting and pastel colors go together nicely.
Intuitive controls
Simple but engaging concept. Lots of space for really cool levels
Cons:
Timer on levels hinders fun more than it adds challenge (for me at least).
Physics interactions are a bit wonky. When running into a platform and jumping at the same time, the jump is cut short.
No restart or undo button when placing platforms.
Suggestions:
Add some more juice (squash and stretch on the cube when jumping, maybe a bit of screen shake).
Have different types of platforms you can place (and that are already placed in the level) - Slippery platforms, spikey platforms, bouncy platforms.