I haven't finished playing yet but for now I can say that the game is really atmospheric - and I mean *really*. The music and sound design are awesome, the vibe pretty spooky. I like the full narration and appreciate that the player can choose between 3 difficulty options, and 2 "levels" of narration. The story seems engaging, I really like the world building. I'd say it's different from the original Kona, but it's still a very nice game. My only issue is with the controls but that might be because I'm using mouse+keyboard, it might be better with a controller. Still, overall it's a very cool game!
I'm a sucker for such games so I won't be objective. That being said, Under the Waves does a lot of things really well: the atmosphere is great, the slow pace of the story - great, the audio-visual side simply awesome. There are some small bugs but the autosave feature works well (very often) so I haven't had to repeat anything yet. It crushed on me once but then re-launched without issues. I love the story so far, it's sad but told really well. 5/5 from me! :)