Awesome music (especially Main Menu) and overall great sounds, although I think they could fit the visuals a little better. With music, I would have liked for the instruments to be less modern on the Overworld ost, but I really enjoyed it anyway. Some minor things with the sfx: stereo sounds for game objects don't work too well (especially footsteps, or flippersteps...) and having a stereo reverb muddies up the landscape where your music can't sit very well on the mix anymore. I also would have liked even the tiniest sfx for water movement, and I would add a bit more low layers on your Enter or Exit water sounds. I like to limit the frequency range near the end of the master chain to mimic retro system's audio better, same with dynamic range. And lastly, I would have loved for sfx to go through a bit of reverb, and EQ'ing everything when you enter water. All this said, I still enjoyed both music and sfx a lot, and they helped me immerse in this beatiful landscape.
Art direction is insane, probably the best one in the jam. It looks great, the animations are beautiful, and the tile sets bring a great level design to shine. It really feels as if this game was already one of the classic metroidvanias back in the day. Great great stuff!
Movement feels nice, teleport is super fun and the hidden rooms are cool to find. Very clever level design! The amount of content you guys made is also very impressive!
Sorry for posting my review so late, I did rate your game among the highest (if no the highest) entry for the jam, I really liked it. Congrats!