Gameplay too basic
People say it's boring without saying why.
The controls and graphics aren't bad. There seems to be no glitches either (except perhaps one last beep from the danger siren when just restarting a stage).
I'm actually divided on the sounds. For one thing, you have satisfactory gun sounds and explosions. But then there's the two stages of alarms that go off. You should have merely played a short clip of the alarms, indicating danger.
But no-those are not the big problems.
It's the gameplay, or lack of it.
There are basically have three kinds of enemies-a tank, a helicopter, and a battleship. That's pretty much it. Every level, the game's difficulty increases simply by increasing the fire rate and armor of the same three vehicles.
And each of the vehicles take the same number of shots to kill (starts at 4 shots, then increases by 1 per level). Each stage is exactly identical to the last-I'm guessing it just loops over and over, meaning that it's repetitive as hell.
There are hundreds, if not thousands of modern vehicles to go after. Heck, you could have even made little terrorist people in little caves to strafe if you wanted to. But no-just three machines. And these machines all fire the same type of weapon.
The title says that it's an Apache. But where are the Apache's other weapons? They come with rockets and hellfire missiles too (make them have some ammunition counts). The chain gun could have also been controlled by the mouse in a forward arc. Upgrades aren't probably necessary.
Granted, this is a SHMUP type game, but Apaches rarely go out on their own just for the pyrotechnics. Where's the mission detail? Where are any friendly troops to help or rescue? There's no storyline, thus there's no point.
But since you've been able to program a functional game up to this point, it shouldn't be too difficult to take it to the next level.