There's a whole lot to like here. The art and sound are top-notch and emulating the classic gameboy feel compliments the gameplay which is just as classic. I'd prefer a GBC style to a GB style as I think the added color would help separate some of the objects on the island and give it a bit more life.
The controls were tight and I appreciate the mid-air turning. Gameplay wise, charting the seas was very ambiguous. I wasn't sure where I was headed or that the "compass" pointed towards an island -- until I realized my compass was broken and didn't always point north.
The ship battles were okay, but I think the health pools are too high. I never lost a battle at sea when I mashed but after sailing blindly, mashing became annoying. The island segments were more fun, though with the insta-kills, it made the health pools seem even more excessive. The biggest let down was that every death brought you back to sea and not the island and it was enough to keep me from progressing past my 3rd island.