Hi, just finished trying out your game. Personally I'm quite afraid of the deep sea, so I was quite tense during the descending part. I was scared something came out of nowhere and attacked me. As another comments said, you managed to build tension very well on the first half, while in the second one, it was quite "boring". The element of surprise was really effective, it caught me off guard a lot. Maybe if those fishes started chasing you, and you could just escape really fast (like activating a turbo or something), the adrenaline of the surprise effect would've lasted longer, and the pace of the game would've been very different. This is just a suggestion tho, it would need some playtesting and stuff. Really a great game.
I enjoyed playing it a lot, good luck with it <333