Damn I wish I could give this game a 6/5 in visuals. Very aesthetically pleasing with matching music.
The concept is pretty cool as well. Simple controls, hard to master gameplay. And the upgrades are pretty neat too.
I like the colour choices - white and green for player bullets, red and yellow for enemies. The brown bullets are kinda questionable, but it does differentiate uncontrollable bullets from controllable ones.
The little banner animations between levels and at the beginning of the game are also a pretty nice touch, gives the game that polished feel.
A fantastic game!
Edit: I also love the small screen shakes whenever you take damage or damage an enemy. It's that one little thing that would really improve the game feel but is also rather hard to implement.