I have lots to say about this game. Some of it's good, some of it is not so good. I want to preface this by saying I do not want you to think that I disliked your game, or that it was somehow bad. On the contrary, this is one of the most ambitious, awesome projects I have seen, but with a few major problems I think get in the way of making it something amazing.
I'll first start with the good. Your atmosphere in this game is unrivaled. I've played a lot of game jam games, and I don't think I've found any that are quite like this. Somehow you manage to capture a haunting, lonely, terrifying feeling from such a simple concept. The fear of the ocean/exploration/unknown is something that is so hauntingly scary and you do a wonderful job of capturing that here. Everything is so immersive, whether that be through the display indicators, the radar, the submarine light, or being inside the submarine.
The scale of your game is absolutely massive. The map feels endless, and the cities are so cool. I love how the underwater city just blends into the environment and works so well to make the game feel natural. The radar really compliments the game as well. It's a really cool concept to only be able to know what's around you every 10 seconds. It's quite unnerving to think you know where you're going, but only for sure once the radar light turns on.
As far as some of the bad things go, direction and control are major flaws I think this game suffers from. I'll talk about each individually.
Having complicated controls is not a bad thing in video games. In fact, in can be quite rewarding to master a complex control scheme. Unfortunately, in this case complex is not good. Most things felt clunky, if not outright bad to control. Specifically, accelerating and decelerating, resetting, and turning left and right. When accelerating, you would have to press space to go in the direction you were facing. When decelerating, rather than stopping, there would be a force applied in the opposite direction of your accelerating (I think?). This made me quit using the deceleration feature and only reset to stop. When I was turning left or right, I felt like the roll should not have changed, and yet it did. I would have to compensate by turning while rolling, which was very uncomfortable. When I was first playing, I assumed you needed to navigate through the underwater cities, which led me to crash into many things because I thought I could fit. Controls being easy to pick up in a game jam game is essential. If a player does not feel like they can control the game, they are going to quit rather quickly.
As far as direction goes, I am not referring to the actual direction of travel, but rather the player's sense of "what am I supposed to do?". I felt that there was very little in the game to tell you what to do except for "go find treasure". On my first attempt at playing, I was trying to get acclimated to the controls which pretty much resulted in my flying around into nothingness. I reset the game and on my second attempt all I did was traverse the closest structures to you. I had no clue what I was supposed to be looking for other than "treasure". On my third attempt, I finally thought to myself, "the radar feature is pretty prominent, maybe I should actually attempt to use it", which led to me discovering a cave and finding the treasure.
I ended up getting 3/10 treasures on that attempt, after about half an hour of playing. (I never found the monster).
With all that being said, do not be discouraged at all by what I have to say. The fact is, I'm writing so much about this because I see a lot of potential in this. The mood, audio, and visuals are phenomenal but the game design and fun are very much lacking. When it comes to game jams, the most important thing is to have a quick hook and easy to understand gameplay. I'm definitely not one to talk, and struggle from this a lot myself as well, but I feel like it's such an important thing that often gets overlooked. (Congrats on being my longest comment ever, I maxed the character limit)