Fun and very chill. The swimming felt good as I continued to upgrade, and I made it to the end and got the final treasure only to die on the way back up, and the final treasure didn't respawn so I was never able to actually collect it. Having some more expensive upgrades or a final win condition to end the game would be nice, by the end I could continue upgrading my oxygen and swim speed, but had no need to do so in order to get to the bottom and back.
I did find that clicking on the upgrade menu still sends a signal to the diver to swim, so if you have high swim speed you can only click the upgrade menu a few times before you have moved too far away and it closes. Also very nice effects for the pickup collection, felt very good.
Overall very good, nice work.