Good visuals. Nice colors and very nice parallax scrolling of backgrounds. The controls are pretty smooth, and the attack feels appropriately hefty. I also like the density of platforming decisions on every screen... it's an engaging little world.
However, it feels a little too hard, a little too soon.
It would be helpful to have some more feedback when the player gets hit, for example some knockback.
Lastly, it would be nice to have a delay of 1-2 seconds after death and before respawning.