Nice job! Really good graphics and sound.
To 7axel7’s suggestions I’d add two things:
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Make the sounds for the players shots different than the baddie’s shots.
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Player movement should follow an acceleration curve. Meaning it starts at 0 velocity and ramps up to max while the player holds the arrow key. This can and should happen pretty fast so it’s a subtle effect but it makes a big difference in how the game feels.