Thank you for testing our game! :)
On the first enemy, it takes 3 hits to destroy it. when you lock on (using the triangle button on the Playstation controller, or "Y" on Xbox), you will get a "health bar" above the enemy ship.
The collision is calculated "triangle perfect" (cause it also applies force on the ship that you hit, which gets especially fun ones you got 4 MGs). Therefore it's a bit harder to hit an enemy than in games that only use bounding volumes for hit detection.
I tagged the download as "Linux" cause there is no dedicated "Wine" button, but I've tested it with Wine and it worked, thus I didn't want to discourage Linux users from trying it out.
Thank you for your kind words, it's nice to read after 1 month of effort of our team :)