The premise of collecting enemies to give yourself a health bar is pretty neat! Almost missed it entirely, because the tutorial was pretty subtle and easy to skip over reading, but I went back and saw it on a second pass (since I had a feeling I was missing something).
The difficult spike between the tutorial and the first proper level is pretty significant, though I did eventually beat the first screen - I died when the boat was chasing me though. Some sort of sound effect to communicate to the player that the TNT box characters are exploding would be nice. At first I thought I killed the enemy by jumping on him, so I died a few times trying again.
What story I saw was simple, but very cute. Can't go wrong with pirates chasing booty.
Nice job, and congrats on submitting your demo!