Whel the game is fun, and fancy. I'd put more enemy colours, more power ups, and change the player movement. It feels so cluncky its not that the game wants you to move so much, its not dynamic.
What I rather do is set to the player an acceleration, a maximum speed and a velocity vector. So that when you press the up arrow you add to your velocity vector your acceleration:
//code example
if uArrow :
v.x += acceleration * cos(angle);
v.y += acceleration * sin(angle);
position.x += v.x;
position.y += v.y;
//end of code
Then it would fell like you are in space, just like in the original asteroids.