A really great game! The concept is unique (at least to me) and felt fresh. Reminded me, a little bit, an underwater level in Sega game "Flintstones" :D I absolutely loved the water splash effect when you dive in/out of the water. The roguelite elements were awesome. Adds desire to continue playing and variation to the game style + gives you more room for future content which is awesome. Kudos for tutorial, it was great and gave clear understanding of what to expect and how to play. I did encounter a big downside tho... At the first big treasure there is like a performance drop. Later in the game same thing happens. When the player dies the slow effect also feels like a performance drop. In theory could be my local issue but maybe worth debugging. The audio & sfx were also very fitting.
Maybe at some point you will decide to add some lighting and IMHO that could bring visuals to a whole next level but maybe your game vision is good as it is. Something to experiment with :)
Great job on the game.