super cool idea! some feedback:
too many particle effects when you kill an enemy, it clutters up the screen and can be confusing. i think if they disappeared faster and moved faster it'd be a much more impactful effect, and not clutter the screen.
the camera felt a little static, maybe moving it based on the player's position and the mouse position, so you can move the mouse to see further. games like Nuclear Throne and Hotline Miami do this. also some screenshake would be nice.
it's possible to get stuck on the outside border. i was just riding around there and got stuck, wasn't able to turn or move out.
audio isn't great either, but it's still better than none. definitely need some rocket thrust sounds in there.
controls are fine, though it feels more like playing a top down shooter than a space shooter. i think Didolino has the right idea, try slowing down the acceleration/deceleration.
all that being said, there's still plenty to love about this game:
the concept is instant to grasp, which is vital for good arcade games. the core loop of going out, shooting bad guys and returning again can be really really fun.
the shop is a very welcome addition, i'm glad you included it. good polish too. all the upgrades make sense and there's really nothing to complain about here. well done!
the fuel system is great. linking health to ammo is really great idea and also prevents people from just spam firing 1000 bullets. terrific stuff.
the art is very clean and presentable. love the little spaceship sprite.
overall there's a lot of potential here and it's a great concept, would love to see you develop it further.