I played your game! Space shooters are fun! Here's a little list of suggestions that I think would improve it:

* I don't like smoothing/inertia on the player in these types of games. I like 'em to feel tight and precicse. This one is a bit floaty coasting to a stop.
* Needs to have difficulty. Ideally, you'd have a hand-made progression of enemy waves, but even some kind of '+1 dude every so often' would help. Right now it gets boring fast with just 1 or 2 enemies on screen.
* Ya know that dude that flies off the top of the screen? I hate him. He needs to stay on the map!
* It doesn't take much to make a background repeat. GIMP is a free art program and has Filter/Map/Make Seamless (I think). Doesn't always look great, but won't be as jarring as it is now.
*Old-school games get old-school mechanics. One-hit kills and player gets a number of lives goes great with this genre!

...And, of course, all the stuff you don't have time to get to in a LD game :wink:

Nice start to a game, I do really like the explosion effect. I won't duplicate the points made already, but I suspect you have learned a bunch about building games quickly and will do a lot better next time :)