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.
Mario Odyssey
AC: Odyssey
Zora sections of Majoras mask are good
Returnal did a great job with their water level
Goonies 2
Mot sure if this counts but Returnal’s final level called Abyssal Scar. One if the few times in a video game where I truly felt way deep under water. Along with all the darkness and terror that entails.
Subnautica
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.
TMNT on the nes
Spyro 2 and 3. Namely Aquaria Towers from 2 and Seashell Shore from 3.
Rayman Legends. Them water levels including the musical ones are amazing!
Glu glu!!
Subnautica. The whole game was built around the idea of exploring underwater and it really shows. Movement in the ocean is very smooth and feels great compared to movement on dry land, which feels very awkward, like you’re controlling a drone with a camera on top.
Assassins Creed: Black Flag. Some of the best water physics ever seen in games.
Metal gear solid 2
Back in the day, Super Mario Odyssey: The Seaside Kingdom and Legend of Zelda: Breath of the Wild comes to mind.