A lot of recoil-based movement games feel way too out of control for me, but this was just perfect, I always felt like I had a handle on controlling the diver. You captured the floaty underwater movement in an incredible way. Whenever I hit a wall I felt like it was due to my own failure and not some issue with the game's movement mechanics.
I would have liked to have been able to hold the mouse to auto fire instead of continuously clicking. The ambient background is nice, but some real music like on the title screen might have made the game feel more lively.
Overall, what was really missing is just... more. More upgrades, more enemies, more powerups, would be awesome to see.