This is a cool interpretation of the theme! I enjoy the random level generation on each dive - it really made each dive feel unique in its exploration, and gave ample reason for including and using the sonar.
The progression is really slow. In the beginning, it can be a struggle to get one or two gold pieces. And, factoring in purchase-to-repair, the progression is almost non-existent for the first several dives. I didn't unlock the upgraded O2 tank because it was taking too long.