Excellently presented, graphics and audio are exceptional, though the background music seemed to fade into the ambience a little bit until the ending scene. I agree with other comments that the intro scene is a little long on successive restarts, and I thought the ending was also a little long.
The sub usually felt good to control, though before getting any upgrades I did manage to spend 27% of my energy getting stuck in a little crevice while scanning the little thing to the left of the start point
It was sometimes a little finicky to get in the right position to scan, so showing some hint of the scan arc could be useful, and it wasn't until almost the end that I noticed the scan percentage on screen, so that could either be placed above the item being scanned, or turned into a bar or radial progress meter over/on the scanned item. Toward the end of the game, scanning as a mechanic seemed to drop off somewhat anyway. The light upgrade didn't seem to be very useful, I never needed it to see and turning it on only seemed to drain the battery and trigger enemy aggression.
I did almost get stuck at the beginning, before I understood that I needed to die to upgrade, I ran out of energy and wasn't able to move, so I had to restart the entire game.
Overall very well made, great game.