Not a bad idea, but could use some work.
For one thing, it's kinda hard to get the hang of. To try out all the ships, etc. You don't really have any idea for how each ship works, and they really do behave quite differently. This is a good thing. But with the long time limit for each level, I ended up restarting it over actually waiting until the level was finished. It would be really nice to have an option to select how long you would like a level to last, either by punching in an integer or just giving a few score/time limits. 15, 25, 50 and 100 pts maybe, and 15, 30 and 60 seconds. More if you want, whatever. Just some variety there would help.
The biggest problem was the two player controls. I mean, QZSD? What were you thinking! They arn't next to eachother, they don't seem to have any order to them (Q and D turn? What?), they pretty much just suck. Just changing them to the more standard WASD would help alot, with W going forward, S going backward, sensibly. Then the second player might actually have a shot.
And, as I'm sure you've heard in other reviews, a single player version would be nice. The AI shouldn't be too bad to write, and it would make a lot of people much happier. Maybe even make a story mode with a tournament or somesuch if you're feeling ambitious. Would add a lot of depth to the game.
Overall, good idea, poorly implemented, hope to see an improved version in the future.