Your game is great, and I agree with that other guy that it'd work beautifully with an eight-track pad. Personally, I like the relative turning system, but if you're going to implement that in a game, it would be preferable to allow the ship to fire at <i>any</i> angle- not just orthogonally or diagonally.

The rest of the game is real nice, and deserves a few more stars than it currently has for that. It's small, simple, eye-catching, and has the potential to become addictive. Good work!