It's honestly incredible to see how good mode7 graphics can look with a modern engine, I'm super inspired by the look you've pulled off. The turtle ship is wonderful, there's a solid little gameplay loop and the sound effects emphasize exactly what they need to. Great job!
If you explore more behaviours in your AI it may make for more interesting exchanges of weapons fire, I'd look into basic boids like movement as a start. The music can get a bit harsh, especially with instrument samples that are more square than sin in so many layers. It could probably be improved by removing layers. Maybe consider separating the palm tree from the island so you can swim past it.