Insanely polished game. great gameplay, it was fun, the concept was good and well executed, good visuals, and audio is good.
- The game is quite difficult but that also makes it rewarding to complete. It encourages exploration, though this could be further improved because when I played I didn't know where to go, and I picked a path too difficult at first and didn't think that the other paths would be any easier.
- There could be some kind of difficulty display on the map, or locking the path to destinations at the start, or in some other way try to guide the player to a good route. I also didn't want to change route after picking one, but tried to complete it. I went down to the pufferfish zone at first, and I found the pufferfish warning time to be too low. I tried reacting to it but still missed at times. I also think the upgrade tree could further be improved.
- The only upgrade that seemed appealing at first was the cannon upgrade, there could be other cannon-related upgrades that don't give you an extra cannon, like increasing fire cooldown, damage and projectile speed, say, separately from an extra cannon. Also more basic health upgrades would be good.
- I also found it annoying when I realized I need to upgrade my ship to proceed, but have to do a detour just to do the same trip again to get back to where I was. This wouldn't be a problem if the route was better guided. If you wanted to retain the exploration aspect you could perhaps add a quick travel feature where you can travel to any location you have unlocked by traveling to it once, but don't gain any gold from it, or maybe you even have to pay to use it.
But seriously good job with this game. It's already amazing as it is.