Visuals are top notch, gameplay is simple, fun and intuitive.
I love how the background represent your health, it's really intuitive.
Most enemies nicely telegraph their attacks so you can dodge it in time, well done!
The only thing that i didn't like are the asteroids that don't explode on there own and you have to trigger them to spawn new enemies.
Here's my feedback:
1. Please, PLEASE, next time export to HTML5/Linux/Mac OS, i couldn't play your game because I'm on Linux, so i had to setup wine prefix to play it!
2. Consider adding camera shake when player hits an enemy and when player receives damage
3. Try adding slow-mo/frame skip for the same actions
4. Add timed powerups like laser and make the spawn more likely when player has low health
I believe this changes will greatly benefit your game, but it's up to you.