Cool game! I like how it goes for a different style than the typical platformer, with more of a shoot-em-up vibe instead. The underwater setting is neat as well, and it did a good job of feeling like a deep sea adventure with fitting music and visuals. I liked the detail of things getting darker as you descend. The scenery was a bit samey though, and as a result I found it hard to orient myself in the world. Regardless, there's a nice variety of enemies, and even some pretty cool bosses!
The one thing I struggled with most is the controls. My keyboard doesn't have a numpad, so I had to get an AutoHotKey script to rebind some keys to actually control the game. It really should support WASD or directional keys. Sometimes the ship's movement would get "stuck" so that when I released all the movement keys it would continue moving in certain directions. Not totally sure if that was the game or the script, but it definitely made things awkward.