There are some capital flaws to the player control that make it frustrating. The horizontal movement in too slow compared to the strength of the jumps. As result the jumping arc feels clunky and stiff. It's especially bad because the game tries to be fast paced.
The enemy placement seems rushed. Most of the time you put them in close areas, and they're so fast that it's difficult to avoid them. In other parts it's just plain awkward like the enemy exactly above the spring in level 3.
Also starting on level 3, there's a couple leaps of faith. The game art is small and the camera is big enough. There's no excuse to put the spikes just below the camera, it's no fault of the player to fall in the spikes because there's no way to know.