Really nice game. For me, the difficulty scales really nicely. It does not get stressy too soon, nor too late. The sprites and other assets are also really well done, considering everything is self-made ^^
For my personal taste, the music could be more intense, considering that the levels are getting progressively more stressful. Also, even though the tutorial is a bit long, after a few tries, I'd say the game is pretty self-explanatory.