I’ll go first. In my opinion Ori and the Will of the Wisps does the water level just right. Luma Pools which is the water area/level does it just right where it’s not too frustrating, not too challenging but also super duper fun. And not to mention the area music is top tier too.
It’s not really a “water level” more like an entire environment, but the newest region in Genshin Impact has some of the best underwater exploration I’ve ever played. It’s rather simple in some ways, but it’s well done.