I like how this is just "The World's Hardest Game" but easier. That said, the later levels are super tough and if you losing all your hearts in any stage you're sent back to the beginning of the game (maybe that could've been a harder mode). The levels are generally well designed, though, as they present the obstacles for you to analyse before jumping in. Difficulty progression is steady, too.
The sprite work is great and feels right for a Game Boy, the music is good with a solid pirate theme, if not a bit repetitive, and the characters, especially Captain O'Greddy, are adorable.
Great work overall!