Dear god, could you possibly make anything worse? Seriously, the gameplay is awful, it sounds like you're trying to destroy my eardrums with the "sound" that comes out of the speakers, even at comparatively low volume levels and the graphics suck as much as the gameplay mechanics.
Right, where do we start with improving this piece, blank canvas aside. Let's assume that this piece is indeed salvageable, which is debatable. I'm looking at the main menu for the game having better drawn icons - zoom in, even if you're still using Paint, as this will give a better finished product when you zoom back out.
Once the visuals have been improved, the space invaders themselves seem alright - more variation might be required for later levels, but without redoing the game mechanics, you're going to get nowhere. Dropping a bomb from each invader every 2-3 seconds gets old quickly and kills off the defender. Players like a challenge, but not this much of one. One or two bombs at a time, from random locations should help. This will allow you to get a much better output and will give the game much more longevity.
Sounds. The music is great on its own, so kudos for the artist who originally created it - thatcomposerguy, if I recall correctly. That aside, you've ramped up the volume to screamer scale and it puts you off so much that you have to play in mute. It's a travesty to have to witness a quality artist's music destroyed like that and as harsh as that may sound, it's just what you've done. On the menus, the preloader / start screen is fine, then you come the menu, where the tune is louder and much more abrasive.
Finally, we come to the laughable High Scores section. Yes, it's a half decent bit of programming, but I can make a more aesthetically pleasing high score table in Excel. Try some sort of background themed around space and then get a decent font and colour that contrasts nicely with that, so you can display the scores. Little touches make all the difference.
[Review Request Club]