It is really challenging, which i like. Its graphics are cute. I saw a few minor quality of life adjustment you might want to add (if you are not making a rage game that is ;) ) when player releases the up button the players upward speed immediately goes to zero, you might want to make it so it only halves the speed, also you might want to make collision a little more forgiving and the spikes look a little like mushrooms you might want to add a shine or some other effect to differentiate it.
But at the end of it all i am only being this harsh because i really liked this game and want to see a full version of it.