This is one of the few games I would sit down and play even if I wasn't rating games for a game jam. Great job. The art is beautiful, particularly the water. Having everything controlled by the mouse makes it easy to pick up.
I really love the mining and upgrading, but not so much the combat. Combat is more difficult and annoying than fun. For one, the gun is placed above the submarine so it's hard to aim. Also, you gotta move in the direction of the enemy. I found myself always going in circles trying to kill one guy. But then a bunch of other monsters would come at me from other directions. So I would just lose health while mining until I go repair. For the jam, I think it would have been better to go without combat and develop the mining even more.
Sometimes its hard to see what's going on. The submarine moves fast and the camera lags behind, so I can't see what's in front of me. Also the lighting should be 360 degrees, not only in front. When mining, I can't see anything because the light is pointing right at the ground. If you want the effect of a spotlight, how about keep the bright spotlight you have now, and add a dimmer light that goes 360 degrees around the sub.
I know it seems like a lot of criticism, but that's only because I am interested in the game. Good work.