a fair game
This game is quite good my dear friend so don't listing to them,
I will give you some pointers :D
Try expanding the screen as i feel the screen is just too small a bit more zoomed out maybe? either way try to put some more different ufo's in it you know bosses, hard to hit or maybe a badass ufo you get the point ;D but try it without unlimited ammo as it could be a challenge when you have to aim more precisely than just spam them and more upgrades
But overall a fair game have some flaws but good hope this give you something to work with:D