You move by firing, which becomes very awkward (especially on a laptop mouse). I'd prefer that movement be separated out from firing.
Also, your exit button is freezing the game forever on being clicked.
I want more, by the way.
The movement system makes it harder than expected, especially if your player isn't familiar with Asteroids the game. Having a basic tutorial graphic for the first minute or so showing the controls and expected action on those controls could help. Otherwise, it plays like an arcade game: easy to start, hard to actually beat.