Thanks for taking the time to play and post. You've given me some very useful feedback I think you're totally right about the mouse cursor in the map screen. Even though any click takes you to the next level it feels weird if you've got a cursor, then suddenly have no cursor.
Yes! You can destroy the spawns. Remember that every time you hit with a bullet it charges up your gun. So if you take a second to destroy the spawns your gun will power up faster and the flying enemies and everything else will become a lot easier.
The flying martians are very sensitive to seismic vibrations. Any walking will disturb them, so if you need a break to recharge your shields you can stop walking and they will stop coming after a few seconds. This trick doesn't work in the boss area though because the drilling machine is constantly shaking the ground.
Also, the name "Children of Apollo" is because the colonists on Mars that you are sent to rescue are the generation of space explorers after the Apollo Moon missions.
Ah yes I couldn't remember if there was a tutorial, if there isn't one, maybe consider adding a quick one? Or to fit the retro style, how about you display a booklet/small guide that comes with games, on the screen that you can flip through? You know, with page numbers, a header and then a simple drawing with a few lines of subtext, displaying the tips you just gave.
Because I was kinda clueless as to what to do in the game (though I guess that fits the theme because 80's games were tough as hell) but you know, you gotta compete with present days games which are often intuitive and easy to understand.
I guess I also didn't have much patience to try out things in the demo, I'm one of those folks that like to jump right into a game and play without reading too much and learn 'as you go'. Perhaps also make the booklet available ingame (somewhere you can always access it), or display it just before the game starts.
But hey, this is just an idea, feel free to do something with it or leave it at that. Anyway, good luck with the game!