You did a really good job with the atmosphere on this one. The song used along with the graphics really sets up a place that is both calming and nerve-wracking, calm enough to allow one to make quick decisions but still nerve-wracking to make things tense and fun.
The game itself is also quite fun! I enjoyed moving around the surface to get the different treasures and the oxygen mechanic really made for a fun challenge. The only thing that can make this experience better is if maybe there was a clearer indication of progression. There is a treasure value that I see on the top-left of the screen, but I guess I was just unsure if this is what is used to keep track of my score in the game. Overall though, I still found this game enjoyable and I especially loved the atmosphere you built with this one.