Yes you are absolutely correct, but I have tried as much I make it fix with the theme, if game becomes laggy, then it may be the problem of the processor. You might find it easy to make this game, as I am not a professional game developer.
And the KRY machine (player spaceship) may stick on the borders of the screen which made you lose the ability to move, and I will fix it later, because I didn’t knew much to make the player stop at the borders of the screen in Game Maker 8, so to make it stop there I used a little code i.e. gravity, friction(which sticks the player), bounce and reverse motion, but for that it might stick there, and the shield is dropped from the small cyborg enemy which comes after 500, the carrier enemy after 20 can only drop health.