Pretty cool game, nice job team, its an entry to be proud of! I really dig the underwater aesthetic and I think the visuals really fit well into the Upside Down theme, everything feels dark and like you are inhabiting a foreign place where the rules of the environment are different. The colors work really well and the little fishes swimming by and glow of certain objects adds a lot to the ambiance. The sound/music fits very nicely overall. I think your take on the theme (in terms of both game mechanic and aesthetic) fits very well.
That being said, I think the game play itself suffers from being too difficult. I think the main reason it missed the mark for me was the lack of consistency in jump angle. Sometimes it went far at a 45 degree angle and sometimes it went straight up, seemingly independent of my input as a player. This resulted in me feeeling like the missed jumps weren't always my fault, which I think is not ideal for a rage game. In a rage game you always want to feel like you messed up because of a lack of skill not from wrestling with the controls. Also, sometimes as devs its a lot easier to beat our own games than it is for a random player, so it might be helpful to have an outside person who is not part of the dev team playtest too. Just some food for thought. Cool entry, with a beautiful aesthetic and great take on the theme, nice work team!!