I've played your game for the last 45 mins or so. And I must say, it's quite fun actually. The whole feeling and especially the sounds remind me alot of the old atari games.
Something you might want to consider though is a manual pause between the levels. You're speeding through each level with very little time for the player to gain a bit of awareness of what is happening.
After having shot the last enemy (which most of the time, is quicker that I realize), the screen goes blank for a split second, the flashy intro appears and before I know it the next level starts.
There's no clue about the amount of points I've scored, how many people I've saved (or didn't save), what level I'm at etc.
I think some extra info, as well as a 'get ready for the next level, press the whatever key to continue' would work well here.

Another thing you really should look into is the way you handle the usernames. I've had the option to add my name to the score list a couple times (I think I even made first place) but each time I did not get any further than 'A'. Please have it so that I can type my name.
I understand it fits the retro feeling of past games, but mind you that it should not be a game on its own.

Lastly, while playing your game, Vista decided to throw me a message that there was an important update to install. Cool, i thought, but dont bother me while I´m playing.
I returned to your game, only to find out that it did not run anymore. Just when I was doing so well...
Alt-tabbing back to windows, should not mean the end of the game.

Two other 'real' bugs:
After looking for a pause button, I discovered that P did the trick. Fortunately there didn't seem to be a way to unpause though. :?

Pressing escape while everything 'warps in', appears to be a great way to let the game crash.

In all it's already a great game. There's still some work left to do, but I'm sure when you iron out these last issues, it will be even better.