So, I got really involved in this game and I came away with a lot of questions.
I seemed to kind of get "locked" in that I needed a lot of money to keep upgrading, but carrying enough money to the next upgrade caused me to go REALLY slow. After a few deaths I changed my strategy to not pick anything on the way down, but gather on the way up. So, I am at my slowest near the surface.
While it's a cute strategy that works, it's not intuitive and goes against the players nature of trying to collect and keep enough gas to the top.
I also found the depths were not more lucrative than the shallows. I expected to see larger and larger clams as I improve my oxygen and speed and can come away with more money.
Also I was confused by Agility. Is that truly my ability to redirect and change direction? Or is it perhaps related to carry weight? I was getting weighed down so quickly with the clams I was carrying, I expected that upgrade to improve my "Purse" or the amount I can carry without getting slowed.
Additionally, there were a few instances where I was ~50% gas, but very deep and slow. I knew I couldn't reach the top. The optimal strategy is to check my phone and wait to drown. Perhaps there is a mechanic in order to preserve the run by ditching some of my clams. Unsure how I'd exactly implement it, but I am imagining players tossing clams desperately trying to reach the surface, but of course they are ditching their money. So, that greed vs survival tension would be at it's highest.