Space shooters are cool ! There's room for improvement though. I'll try not to repeat what was said below !
I couldn't avoid the homing missiles, they were way too fast and agile ! Since they blend a lot inside the waves of bullets coming from enemies you can't see them before they hit you.
Enemies should not stay nor shoot from off screen ! You don't know what you're shooting at because of this and it removes the satisfaction of seeing them blow up !
If you're going to play a lot of sounds from a single source (in your case, the lasers you shoot), you should pick something with a lower pitch, and add some pitch variation (you multiply the base pitch by a random number between something like 0.9 and 1.1). It removes a lot of the fatigue you get from hearing the same sound over and over !
You should check https://www.bfxr.net/ It's a great tool to produce retro sounds fast !
Cheers !