Haven't played the ST version yet!! ( Is this release Falcon compatible? )

I have however played the 7800 version, while graphically limited the gameplay is there! and there is quite a lot of game to be had! lots of different enemies, waves, aerial, ground targets, tanks, end of level bosses! Must have been quite some progression from Space Invaders back in '82!

I'd recommend checking out the 'similar' title from Rainbow Arts called 'Sky Fighter'

cheers  8-)