Ok, I really love the story and it's kinda fun.
But it's missing a ton of juice, you should add camera shake for shooting, hitting an enemy, taking damage
And I don't know can you do that in GDevelop, but some particles for shooting, damaging an enemy, killing an enemy and dying, would look cool, but if you can't do that, then yeah.
Also you should add a lot more feedback for taking damage, those particles, that camera shake and maybe a red flash of the screen.
Also the pixel size, the problem isn't that bad in this game, because of the pixel perfect camera, but the larger pixels are still noticeable, and it doesn't look good, especially the background has way too big pixels.
And for some reason when you die, you go to the settings menu, it should just start back to the game, or at least just to the normal menu.
And the gun doesn't point at the cursor, little bit off, you shoot to the cursor, but the gun facing the wrong way irratiates me, and some times even confuses.