Controls feel really nice and overall it's a nice idea!
Just a few tips:
- Be a bit more forgiving with the hitboxes, they're a bit too big and the player might hit a spot where the sprite doesn't reach;
- Make the enemies stand out, a black outline on a black background can confuse players and make them think that the enemies are smaller than they are;
-Spawn more bullets and reward the player for shooting down enemies by giving them more bullets, also make the player start with some bullets, because this way the player feels like they should save their ammo and not use it;
These are just a few suggestions :)
P.S. the explosion effect looks really good!