Late reply, but I think this is a good example of how a couple easy improvements could've greatly improved your game.
When I first started playing I was trying use use the arrow keys and spacebar to fire, which basically meant I couldn't move diagonally. Customizable controls, not using the spacebar for firing, autofire or mouse controls would've solved that.
It does look very nice though and seems technically impressive. Perhaps you could make a more interesting upgrade system, add more enemies and level variety, and turn it into something great.