Very fun game. The way you can keep going as you play the game and unlock more areas as well as the size of the map is great. I ended up playing it for half an hour before realizing I had more games to rate lol. I managed to find four trophies but couldn't find a way to unlock the golden one.
Only piece of feedback I have is to add a map that can show you what you've seen, as well as where you are / where your tube is. The additional dialogue throughout the game as you unlock more and more of the map is great as well.
Music fits the game really well, definitely has its underwater feel to it.
As of fixes I would just say maybe make it so your tube doesn't get stuck on corners at times. (Maybe round the corners a bit?) Very fun game, 10/10 would love to see the map expend even more.
And just as a general question, how many coins are there in total / how big is the map? I got to around 200 coins.