I personally love low stakes exploration gameplay, which tends to require the art, movement gamefeel, and level design to carry it, and you did an amazing job on all counts (edit: I got so focused on the visuals I forgot to mention MUSIC it's a perfect match, love the restrained vibrato, and the hi-hat detailing did not escape my notice) . I have a bit of commentary about some specifics, forgive me if it gets long-winded. (Also, not intended as criticism, just some subjects I'm deeply fascinated with.)
You used quite a lot of dithering for shading, and I think it worked well in some places but not in others. In the opening cutscene, I think it looked great on the hand and seagull, and while it makes logical sense for sand on the controls / Press Start screen, it makes the text harder to read. In the first scene when starting the gameplay, it is a bit distracting in the sky and ocean surface, due to the ordered and patterned nature of the Bayer matrix. But for this reason, I think it works well on architectural objects like the columns. There's alternative techniques like Blue Noise and Interleaved Gradient Noise that work well to disrupt pattern recognition in gradients, and I wonder if these have potential with the Game Boy resolution / palette limitations.
That said, the organic shading on the rocks is perfect, and the bricks look great too. I like the wiggly animation of the algae (I think it's algae?), the underwater creatures like sharks and schools of fish are delightful, the bubbles and currents, all these animations really help make the setting come alive. Good use of parallax. The hazards starting in the second stage are easy to read, once you learn what they are. Harder to read in some spots in the third stage due to lower contrast. Leaving corpses behind is a nice touch lol.
I got partway through the third stage but have to leave it for now due to IRL commitments. I will definitely pick this back up later though, it's really a fantastic entry.
