The addition of the lunar islands was a nice touch to the game, but i'm still on the fence about how sea exploration and sea combat is fun and entertaining. My critique is based solely on playing alone, and I mention this because this might be a reason I find the ocean in DST so frustrating.
The ships are clunky to navigate due to it's speed and size, and easy to damage with the numerous basalt that clutter the ocean. Damage taken by the boat can be considered annoying to fix since it takes four pieces of wood and proper mousing over to perform the action. As your ship gets more damaged or more cluttered, it becomes harder to mouse over the spouts. there is a huge resource scale to start exploration and time investment to explore the ocean due to the basalt and likelihood of running out of resources.
With combat, the main tactic of the game is to kite and swipe at your enemy/enemies. When on a ship, you almost forced to tank damage when facing numerous enemies and is impossible to kite boat damage since navigation is so slow. Combined with the difficulty in repairing the ship, you are forced to spend much of your time fixing the ship. Often times, the enemy has already begun creating more water spouts on your ship.
I like the addition of more creatures to the vast and mostly empty world of the ocean, but like the antlion, i feel some creatures just make the experience less enjoyable (ex. I'm look at you, cookie cutters) and offer little to no reward to make that experience enjoyable (ex. getting the salt). Keep up the good work, Klei, and continue to improve the game. I hope in the future seafaring and the mobs that inhabit the ocean offer a rewarding and game enriching experience that adds nicely to the land and cave features. I know the sea is still being worked on and it's not perfect yet, but these are my views on the July 2020 state of the ocean.